Rare-earth diantimondes exhibit coupling between structural and electronic orders, which are tunable under pressure and temperature. Here we present the discovery of a new polymorph of LaSb2 stabilized in thin films synthesized using molecular beam epitaxy. Using diffraction, electron microscopy, and first-principles calculations we identify a YbSb2-type monoclinic lattice as a yet-uncharacterized stacking configuration. The material hosts superconductivity with a Tc = 2 K, which is enhanced relative to the bulk ambient phase, and a long superconducting coherence length of 1730 Å. This result highlights the potential thin film growth has in stabilizing novel stacking configurations in quasi-two-dimensional compounds with competing layered structures.
\nSquare-net tellurides host an array of electronic ground states and commonly exhibit charge-density-wave ordering. Here, we report the epitaxy of DyTe_(2\u2212\u03b4) on atomically flat MgO (001) using molecular beam epitaxy. The films are single phase and highly oriented, as evidenced by transmission electron microscopy and X-ray diffraction measurements. Epitaxial strain is evident in films and is relieved as the thickness increases up to a value of approximately 20 quintuple layers. Diffraction features associated with a supercell in the films are resolved, which is coupled with Te-deficiency. First principles calculations attribute the formation of this defect lattice to nesting conditions in the Fermi surface, which produce a periodic occupancy of the conducting Te square-net and open a band gap at the chemical potential. This work establishes the groundwork for exploring the role of strain in tuning the electronic and structural phases of epitaxial square-net tellurides and related compounds.
", "doi": "10.1021/acs.cgd.3c00755", "issn": "1528-7483", "publisher": "American Chemical Society", "publication": "Crystal Growth & Design", "publication_date": "2024-01-03", "series_number": "1", "volume": "24", "issue": "1", "pages": "115-121" }, { "id": "authors:gb9bh-d1x59", "collection": "authors", "collection_id": "gb9bh-d1x59", "cite_using_url": "https://authors.library.caltech.edu/records/gb9bh-d1x59", "type": "article", "title": "Spin and valley-polarized multiple Fermi surfaces of \u03b1-RuCl\u2083/bilayer graphene heterostructure", "author": [ { "family_name": "Kim", "given_name": "Soyun", "orcid": "0009-0001-0333-7181", "clpid": "Kim-Soyun" }, { "family_name": "Hong", "given_name": "Jeonghoon", "orcid": "0000-0003-4708-2536", "clpid": "Hong-Jeonghoon" }, { "family_name": "Watanabe", "given_name": "Kenji", "orcid": "0000-0003-3701-8119", "clpid": "Watanabe-Kenji" }, { "family_name": "Taniguchi", "given_name": "Takashi", "orcid": "0000-0002-1467-3105", "clpid": "Taniguchi-Takashi" }, { "family_name": "Joseph", "given_name": "Falson", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kim", "given_name": "Jeongwoo", "orcid": "0000-0002-4070-1878", "clpid": "Kim-Jeongwoo" }, { "family_name": "Kim", "given_name": "Youngwook", "orcid": "0000-0001-9544-5691", "clpid": "Kim-Youngwook" } ], "abstract": "We report the transport properties of \u03b1-RuCl\u2083/bilayer graphene heterostructures, where carrier doping is induced by a work function difference, resulting in distinct electron and hole populations in \u03b1-RuCl\u2083 and bilayer graphene, respectively. Through a comprehensive analysis of multi-channel transport signatures, including Hall measurements and quantum oscillation, we unveil significant band modifications within the system. In particular, we observe the emergence of spin and valley-polarized multiple hole-type Fermi pockets, originating from the spin-selective band hybridization between \u03b1-RuC\u20833 and bilayer graphene, breaking the spin degree of freedom. Unlike the \u03b1-RuCl\u2083/monolayer graphene system, the presence of different hybridization strengths between \u03b1-RuCl\u2083 and the top and bottom graphene layers leads to an asymmetric behavior of the two layers, confirmed by effective mass experiments, resulting in the manifestation of valley-polarized Fermi pockets. These compelling findings establish \u03b1-RuCl\u2083 proximitized to bilayer graphene as an outstanding platform for engineering its unique low-energy band structure.
", "doi": "10.1063/5.0170810", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2023-10-01", "series_number": "17", "volume": "123", "issue": "17", "pages": "173101" }, { "id": "authors:61d5h-n1a97", "collection": "authors", "collection_id": "61d5h-n1a97", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221128-494761600.59", "type": "article", "title": "A highly anisotropic polymorph", "author": [ { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" } ], "abstract": "Superconductivity with an anisotropy is revealed in a layered material. This result points towards a version of superconductivity where spin\u2013orbit interactions produce a material that is resilient to external magnetic fields.", "doi": "10.1038/s41567-022-01824-4", "issn": "1745-2473", "publisher": "Nature Publishing Group", "publication": "Nature Physics", "publication_date": "2023-01", "series_number": "1", "volume": "19", "issue": "1", "pages": "19-20" }, { "id": "authors:eg7x4-v1q90", "collection": "authors", "collection_id": "eg7x4-v1q90", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210409-151541040", "type": "article", "title": "Competing correlated states around the zero-field Wigner crystallization transition of electrons in two dimensions", "author": [ { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Sodemann", "given_name": "I.", "orcid": "0000-0002-1824-5167", "clpid": "Sodemann-Villadiego-Inti" }, { "family_name": "Skinner", "given_name": "B.", "orcid": "0000-0003-0774-3563", "clpid": "Skinner-Brian" }, { "family_name": "Tabrea", "given_name": "D.", "orcid": "0000-0001-7656-0627", "clpid": "Tabrea-Daniela" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "von Klitzing", "given_name": "K.", "orcid": "0000-0002-1720-7396", "clpid": "von-Klitzing-Klaus" }, { "family_name": "Smet", "given_name": "J. H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-Jurgen-H" } ], "abstract": "The competition between kinetic energy and Coulomb interactions in electronic systems leads to complex many-body ground states with competing orders. Here we present zinc oxide-based two-dimensional electron systems as a high-mobility system to study the low-temperature phases of strongly interacting electrons. An analysis of the electronic transport provides evidence for competing correlated metallic and insulating states with varying degrees of spin polarization. Some features bear quantitative resemblance to quantum Monte Carlo simulation results, including the transition point from the paramagnetic Fermi liquid to Wigner crystal and the absence of a Stoner transition. At very low temperatures, we resolve a non-monotonic spin polarizability of electrons across the phase transition, pointing towards a low spin phase of electrons, and a two-order-of-magnitude positive magnetoresistance that is challenging to understand within traditional metallic transport paradigms. This work establishes zinc oxide as a platform for studying strongly correlated electrons in two dimensions.", "doi": "10.1038/s41563-021-01166-1", "issn": "1476-1122", "publisher": "Nature Publishing Group", "publication": "Nature Materials", "publication_date": "2022-03", "series_number": "3", "volume": "21", "issue": "3", "pages": "311-316" }, { "id": "authors:v9xwe-9rq88", "collection": "authors", "collection_id": "v9xwe-9rq88", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211001-212811372", "type": "article", "title": "Ising pairing in atomically thin superconductors", "author": [ { "family_name": "Zhang", "given_name": "Ding", "orcid": "0000-0002-8334-8349", "clpid": "Zhang-Ding" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" } ], "abstract": "Ising-type pairing in atomically thin superconducting materials has emerged as a novel means of generating devices with resilience to a magnetic field applied parallel to the two-dimensional (2D) plane. In this mini-review, we canvas the state of the field by giving a historical account of 2D superconductors with strongly enhanced in-plane upper critical fields, together with the type-I and type-II Ising pairing mechanisms. We highlight the vital role of spin\u2013orbit coupling in these superconductors and discuss other effects such as symmetry breaking, atomic thicknesses, etc. Finally, we summarize the recent theoretical proposals and highlight the open questions, such as exploring topological superconductivity in these systems and looking for more materials with Ising pairing.", "doi": "10.1088/1361-6528/ac238d", "issn": "0957-4484", "publisher": "IOP", "publication": "Nanotechnology", "publication_date": "2021-12-10", "series_number": "50", "volume": "32", "issue": "50", "pages": "Art. No. 502003" }, { "id": "authors:nbbg6-grh95", "collection": "authors", "collection_id": "nbbg6-grh95", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220816-403553000", "type": "article", "title": "Microwave response of interacting oxide two-dimensional electron systems", "author": [ { "family_name": "Tabrea", "given_name": "D.", "orcid": "0000-0001-7656-0627", "clpid": "Tabrea-Daniela" }, { "family_name": "Dmitriev", "given_name": "I. A.", "orcid": "0000-0003-1370-6355", "clpid": "Dnitriev-Ivan-A" }, { "family_name": "Dorozhkin", "given_name": "S. I.", "clpid": "Dorozhkin-S-I" }, { "family_name": "Gorshunov", "given_name": "B. P.", "orcid": "0000-0002-6534-1880", "clpid": "Gorshunov-Boris-P" }, { "family_name": "Boris", "given_name": "A. V.", "clpid": "Boris-A-V" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "von Klitzing", "given_name": "K.", "orcid": "0000-0002-1720-7396", "clpid": "von-Klitzing-Klaus" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" } ], "abstract": "We present an experimental study on microwave illuminated high mobility MgZnO/ZnO based two-dimensional electron systems with different electron densities and, hence, varying Coulomb interaction strength. The photoresponse of the low-temperature dc resistance in perpendicular magnetic field is examined in low and high density samples over a broad range of illumination frequencies. In low density samples a response due to cyclotron resonance (CR) absorption dominates, while high-density samples exhibit pronounced microwave-induced resistance oscillations (MIRO). Microwave transmission experiments serve as a complementary means of detecting the CR over the entire range of electron densities and as a reference for the band mass unrenormalized by interactions. Both CR and MIRO-associated features in the resistance permit extraction of the effective mass of electrons but yield two distinct values. The conventional cyclotron mass representing center-of-mass dynamics exhibits no change with density and coincides with the band electron mass of bulk ZnO, while MIRO mass reveals a systematic increase with lowering electron density consistent with renormalization expected in interacting Fermi liquids.", "doi": "10.1103/physrevb.102.115432", "issn": "2469-9950", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2020-09-15", "series_number": "11", "volume": "102", "issue": "11", "pages": "Art. No. 115432" }, { "id": "authors:p88c1-pf734", "collection": "authors", "collection_id": "p88c1-pf734", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200710-122520543", "type": "article", "title": "Quasiparticle Tunneling across an Exciton Condensate", "author": [ { "family_name": "Zhang", "given_name": "Ding", "orcid": "0000-0002-8334-8349", "clpid": "Zhang-Ding" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Schmult", "given_name": "Stefan", "clpid": "Schmult-S" }, { "family_name": "Dietsche", "given_name": "Werner", "clpid": "Dietsche-W" }, { "family_name": "Smet", "given_name": "Jurgen H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" } ], "abstract": "The bulk properties of the bilayer quantum Hall state at total filling factor one have been intensively studied in experiment. Correlation induced phenomena such as Josephson-like tunneling and zero Hall resistance have been reported. In contrast, the edge of this bilayer state remains largely unexplored. Here, we address this edge physics by realizing quasiparticle tunneling across a quantum point contact. The tunneling manifests itself as a zero bias peak that grows with decreasing temperature. Its shape agrees quantitatively with the formula for weak quasiparticle tunneling frequently deployed in the fractional quantum Hall regime in single layer systems, consistent with theory. Interestingly, we extract a fractional charge of only a few percent of the free electron charge, which may be a signature of the theoretically predicted leakage between the chiral edge and the bulk mediated by gapless excitations.", "doi": "10.1103/physrevlett.124.246801", "issn": "0031-9007", "publisher": "American Physical Society", "publication": "Physical Review Letters", "publication_date": "2020-06-19", "series_number": "24", "volume": "124", "issue": "24", "pages": "Art. No. 246801" }, { "id": "authors:nt4tf-wvz92", "collection": "authors", "collection_id": "nt4tf-wvz92", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200331-120907369", "type": "article", "title": "Type-II Ising pairing in few-layer stanene", "author": [ { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Xu", "given_name": "Yong", "orcid": "0000-0002-4844-2460", "clpid": "Xu-Yong" }, { "family_name": "Liao", "given_name": "Menghan", "orcid": "0000-0001-9108-3013", "clpid": "Liao-Menghan" }, { "family_name": "Zang", "given_name": "Yunyi", "orcid": "0000-0002-1047-4889", "clpid": "Zang-Yunyi" }, { "family_name": "Zhu", "given_name": "Kejing", "clpid": "Zhu-Kejing" }, { "family_name": "Wang", "given_name": "Chong", "clpid": "Wang-Chong" }, { "family_name": "Zhang", "given_name": "Zetao", "clpid": "Zhang-Zetao" }, { "family_name": "Liu", "given_name": "Hongchao", "orcid": "0000-0003-0331-3814", "clpid": "Liu-Hongchao" }, { "family_name": "Duan", "given_name": "Wenhui", "orcid": "0000-0001-9685-2547", "clpid": "Duan-Wenhui" }, { "family_name": "He", "given_name": "Ke", "orcid": "0000-0001-6787-3453", "clpid": "He-Ke" }, { "family_name": "Liu", "given_name": "Haiwen", "orcid": "0000-0002-0007-3117", "clpid": "Liu-Haiwen" }, { "family_name": "Smet", "given_name": "Jurgen H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" }, { "family_name": "Zhang", "given_name": "Ding", "orcid": "0000-0002-8334-8349", "clpid": "Zhang-Ding" }, { "family_name": "Xue", "given_name": "Qi-Kun", "orcid": "0000-0002-4129-1284", "clpid": "Xue-Qi-Kun" } ], "abstract": "Spin-orbit coupling has proven indispensable in the realization of topological materials and, more recently, Ising pairing in two-dimensional superconductors. This pairing mechanism relies on inversion symmetry\u2013breaking and sustains anomalously large in-plane polarizing magnetic fields whose upper limit is predicted to diverge at low temperatures. Here, we show that the recently discovered superconductor few-layer stanene, epitaxially strained gray tin (\u03b1-Sn), exhibits a distinct type of Ising pairing between carriers residing in bands with different orbital indices near the \u0393-point. The bands are split as a result of spin-orbit locking without the participation of inversion symmetry\u2013breaking. The in-plane upper critical field is strongly enhanced at ultralow temperature and reveals the predicted upturn.", "doi": "10.1126/science.aax3873", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2020-03-27", "series_number": "6485", "volume": "367", "issue": "6485", "pages": "1454-1457" }, { "id": "authors:czbfv-vze17", "collection": "authors", "collection_id": "czbfv-vze17", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200403-115231359", "type": "article", "title": "Ballistic transport in periodically modulated MgZnO/ZnO two-dimensional electron systems", "author": [ { "family_name": "Tanaka", "given_name": "K.", "orcid": "0000-0003-1191-5639", "clpid": "Tanaka-Kazunari" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Uchida", "given_name": "M.", "orcid": "0000-0002-0735-8844", "clpid": "Uchida-Masaki" }, { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Ye", "given_name": "J. T.", "clpid": "Ye-J-T" }, { "family_name": "Iwasa", "given_name": "Y.", "clpid": "Iwasa-Y" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Smet", "given_name": "J. H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "We report the fabrication of both antidot lattices and unidirectional stripe patterns upon molecular beam epitaxy grown MgZnO/ZnO heterostructures. The magnetoresistance of these high mobility devices exhibits commensurability oscillations associated with ballistic transport of carriers executing orbital motion within the geometry of the imposed modulation.", "doi": "10.1063/1.5121005", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2019-10-07", "series_number": "15", "volume": "115", "issue": "15", "pages": "Art. No. 153101" }, { "id": "authors:j7sqt-0ha59", "collection": "authors", "collection_id": "j7sqt-0ha59", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200403-072428191", "type": "article", "title": "Phase transitions at \u03bd = 5\u22152 in ZnO-based heterostructures", "author": [ { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" } ], "abstract": "The ability to control the orbital degrees of freedom in high mobility two-dimensional electron systems could open the door to tuning novel phase transitions between strongly correlated states of matter. In these proceedings, we present magnetotransport data of MgZnO/ZnO-based two-dimensional electron systems to study the phase transitions at Landau filling \u03bd\u202f=\u202f5\u22152. A rich cascade of phase transitions is resolved as we modify the polarization of carriers between the N\u202f=\u202f1 \u2193 and 0 \u2191 levels by rotating the sample within a magnetic field. These include a gapped fractional quantum Hall state in close proximity to compressible and anisotropic phases, providing evidence for a delicate competition of a manifold of correlated states that are present at fractional fillings, and whose nature is yet to be fully understood. Note: Contribution to proceedings of Physics at the Nanoscale 2018, in dedication to Professor Tapash Chakraborty.", "doi": "10.1016/j.physe.2019.01.027", "issn": "1386-9477", "publisher": "Elsevier", "publication": "Physica E", "publication_date": "2019-06", "volume": "110", "pages": "49-51" }, { "id": "authors:qy4bv-cy749", "collection": "authors", "collection_id": "qy4bv-cy749", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144732429", "type": "article", "title": "Quantized conductance of one-dimensional strongly correlated electrons in an oxide heterostructure", "author": [ { "family_name": "Hou", "given_name": "H.", "clpid": "Hou-H" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Liao", "given_name": "Jun-Wei", "clpid": "Liao-Jun-Wei" }, { "family_name": "Smith", "given_name": "L. W.", "clpid": "Smith-L-W" }, { "family_name": "Kos", "given_name": "D.", "clpid": "Kos-D" }, { "family_name": "Griffiths", "given_name": "J. P.", "clpid": "Griffiths-J-P" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "Ford", "given_name": "C. J. B.", "clpid": "Ford-C-J-B" } ], "abstract": "Oxide heterostructures are versatile platforms with which to research and create novel functional nanostructures. We successfully develop one-dimensional (1D) quantum-wire devices using quantum point contacts on MgZnO/ZnO heterostructures and observe ballistic electron transport with conductance quantized in units of 2e\u00b2/\u210e. Using dc-bias and in-plane field measurements, we find that the g factor is enhanced to around 6.8, more than three times the value in bulk ZnO. We show that the effective mass m^\u2217 increases as the electron density decreases, resulting from the strong electron-electron interactions. In this strongly interacting 1D system we study features matching the \"0.7\" conductance anomalies up to the fifth subband. This Rapid Communication demonstrates that high-mobility oxide heterostructures such as this can provide good alternatives to conventional III-V semiconductors in spintronics and quantum computing as they do not have their unavoidable dephasing from nuclear spins. This paves a way for the development of qubits benefiting from the low defects of an undoped heterostructure together with the long spin lifetimes achievable in silicon.", "doi": "10.1103/physrevb.99.121302", "issn": "2469-9950", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2019-03-15", "series_number": "12", "volume": "99", "issue": "12", "pages": "Art. No. 121302(R)" }, { "id": "authors:gpjy5-fjn79", "collection": "authors", "collection_id": "gpjy5-fjn79", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144732537", "type": "article", "title": "Andreev Reflection at the Interface with an Oxide in the Quantum Hall Regime", "author": [ { "family_name": "Kozuka", "given_name": "Yusuke", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Sakaguchi", "given_name": "Atsushi", "clpid": "Sakaguchi-Atsushi" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Tsukazaki", "given_name": "Atsushi", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "Masashi", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "Quantum Hall/superconductor junctions have been an attractive topic as the two macroscopically quantum states join at the interface. Despite longstanding efforts, however, experimental understanding of this system has not been settled yet. One of the reasons is that most semiconductors hosting high-mobility two-dimensional electron systems (2DES) usually form Schottky barriers at the metal contacts, preventing efficient proximity between the quantum Hall edge states and Cooper pairs. Only recently have relatively transparent 2DES/superconductor junctions been investigated in graphene. In this study, we propose another material system for investigating 2DES/superconductor junctions, that is ZnO-based heterostructure. Due to the ionic nature of ZnO, a Schottky barrier is not effectively formed at the contact with a superconductor MoGe, as evidenced by the appearance of Andreev reflection at low temperatures. With applying magnetic field, while clear quantum Hall effect is observed for ZnO 2DES, conductance across the junction oscillates with the filling factor of the quantum Hall states. We find that Andreev reflection is suppressed in the well developed quantum Hall regimes, which we interpret as a result of equal probabilities of normal and Andreev reflections as a result of multiple Andreev reflection at the 2DES/superconductor interface.", "doi": "10.7566/jpsj.87.124712", "issn": "0031-9015", "publisher": "Physical Society of Japan", "publication": "Journal of the Physical Society of Japan", "publication_date": "2018-12-15", "series_number": "12", "volume": "87", "issue": "12", "pages": "Art. No. 124712" }, { "id": "authors:bpefp-ac587", "collection": "authors", "collection_id": "bpefp-ac587", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144732751", "type": "article", "title": "Composite fermion liquid to Wigner solid transition in the lowest Landau level of zinc oxide", "author": [ { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "McCollam", "given_name": "A.", "clpid": "McCollam-A" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Bruin", "given_name": "J.", "clpid": "Briun-J" }, { "family_name": "Zeitler", "given_name": "U.", "clpid": "Zeitler-U" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "Interactions between the constituents of a condensed matter system can drive it through a plethora of different phases due to many-body effects. A prominent platform for it is a dilute two-dimensional electron system in a magnetic field, which evolves intricately through various gaseous, liquid and solid phases governed by Coulomb interaction. Here we report on the experimental observation of a phase transition between the composite fermion liquid and adjacent magnetic field induced phase with a character of Wigner solid. The experiments are performed in the lowest Landau level of a MgZnO/ZnO two-dimensional electron system with attributes of both a liquid and a solid. An in-plane magnetic field component applied on top of the perpendicular magnetic field extends the Wigner-like phase further into the composite fermion liquid phase region. Our observations indicate the direct competition between a composite fermion liquid and a Wigner solid formed either by electrons or composite fermions.", "doi": "10.1038/s41467-018-06834-6", "pmcid": "PMC6195604", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2018-12", "volume": "9", "pages": "Art. No. 4356" }, { "id": "authors:29e84-p9r70", "collection": "authors", "collection_id": "29e84-p9r70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144732177", "type": "article", "title": "A cascade of phase transitions in an orbitally mixed half-filled Landau level", "author": [ { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Tabrea", "given_name": "Daniela", "clpid": "Tabrea-Daniela" }, { "family_name": "Zhang", "given_name": "Ding", "orcid": "0000-0002-8334-8349", "clpid": "Zhang-Ding" }, { "family_name": "Sodemann", "given_name": "Inti", "clpid": "Sodemann-Inti" }, { "family_name": "Kozuka", "given_name": "Yusuke", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "Atsushi", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "Masashi", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "von Klitzing", "given_name": "Klaus", "orcid": "0000-0002-1720-7396", "clpid": "von-Klitzing-Klaus" }, { "family_name": "Smet", "given_name": "Jurgen H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-Jurgen-H" } ], "abstract": "Half-filled Landau levels host an emergent Fermi liquid that displays instability toward pairing, culminating in a gapped even-denominator fractional quantum Hall ground state. While this pairing may be probed by tuning the polarization of carriers in competing orbital and spin degrees of freedom, sufficiently high quality platforms offering such tunability remain few. We explore the ground states at filling factor \u03bd = 5/2 in ZnO-based two-dimensional electron systems through a forced intersection of opposing spin branches of Landau levels taking quantum numbers N = 1 and 0. We reveal a cascade of phases with distinct magnetotransport features including a gapped phase polarized in the N = 1 level and a compressible phase in N = 0, along with an unexpected Fermi liquid, a second gapped, and a strongly anisotropic nematic-like phase at intermediate polarizations when the levels are near degeneracy. The phase diagram is produced by analyzing the proximity of the intersecting levels and highlights the excellent reproducibility and controllability that ZnO offers for exploring exotic fractionalized electronic phases.", "doi": "10.1126/sciadv.aat8742", "pmcid": "PMC6140610", "issn": "2375-2548", "publisher": "American Association for the Advancement of Science", "publication": "Science Advances", "publication_date": "2018-09-14", "series_number": "9", "volume": "4", "issue": "9", "pages": "Art. No. eaat8742" }, { "id": "authors:952k8-7qt74", "collection": "authors", "collection_id": "952k8-7qt74", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144732315", "type": "article", "title": "A review of the quantum Hall effects in MgZnO/ZnO heterostructures", "author": [ { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kawasaki", "given_name": "Masashi", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "This review visits recent experimental efforts on high mobility two-dimensional electron systems (2DES) hosted at the Mg_xZn_(1-x}O/ZnO heterointerface. We begin with the growth of these samples, and highlight the key characteristics of ozone-assisted molecular beam epitaxy required for their production. The transport characteristics of these structures are found to rival that of traditional semiconductor material systems, as signified by the high electron mobility (\u00b5 > 1000 000 cm\u00b2 Vs\u207b\u00b9) and rich quantum Hall features. Owing to a large effective mass and small dielectric constant, interaction effects are an order of magnitude stronger in comparison with the well studied GaAs-based 2DES. The strong correlation physics results in robust Fermi-liquid renormalization of the effective mass and spin susceptibility of carriers, which in turn dictates the parameter space for the quantum Hall effect. Finally, we explore the quantum Hall effect with a particular emphasis on the spin degree of freedom of carriers, and how their large spin splitting allows control of the ground states encountered at ultra-low temperatures within the fractional quantum Hall regime. We discuss in detail the physics of even-denominator fractional quantum Hall states, whose observation and underlying character remain elusive and exotic.", "doi": "10.1088/1361-6633/aaa978", "issn": "0034-4885", "publisher": "IOP", "publication": "Reports on Progress in Physics", "publication_date": "2018-05", "series_number": "5", "volume": "81", "issue": "5", "pages": "Art. No. 056501" }, { "id": "authors:8m0wc-e5919", "collection": "authors", "collection_id": "8m0wc-e5919", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144732644", "type": "article", "title": "Nonlinear response of a MgZnO/ZnO heterostructure close to zero bias", "author": [ { "family_name": "Shi", "given_name": "Q.", "clpid": "Shi-Q" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Zudov", "given_name": "M. A.", "clpid": "Zudov-M-A" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "Smet", "given_name": "J.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" } ], "abstract": "We report on magnetotransport properties of a MgZnO/ZnO heterostructure subjected to weak direct currents. We find that in the regime of overlapping Landau levels, the differential resistivity acquires a quantum correction proportional to both the square of the current and the Dingle factor. The analysis shows that the correction to the differential resistivity is dominated by a current-induced modification of the electron distribution function and allows us to access both quantum and inelastic scattering rates.", "doi": "10.1103/physrevb.96.125401", "issn": "2469-9950", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2017-09-15", "series_number": "12", "volume": "96", "issue": "12", "pages": "Art. No. 125401" }, { "id": "authors:rjtfa-4s754", "collection": "authors", "collection_id": "rjtfa-4s754", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144732864", "type": "article", "title": "Observation of anomalous Hall effect in a non-magnetic two-dimensional electron system", "author": [ { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Mishchenko", "given_name": "A. S.", "clpid": "Mishchenko-A-S" }, { "family_name": "Bahramy", "given_name": "M. S.", "clpid": "Bahramy-M-S" }, { "family_name": "Ernst", "given_name": "A.", "clpid": "Ernst-A" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Nagaosa", "given_name": "N.", "clpid": "Nagaosa-N" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "Anomalous Hall effect, a manifestation of Hall effect occurring in systems without time-reversal symmetry, has been mostly observed in ferromagnetically ordered materials. However, its realization in high-mobility two-dimensional electron system remains elusive, as the incorporation of magnetic moments deteriorates the device performance compared to non-doped structure. Here we observe systematic emergence of anomalous Hall effect in various MgZnO/ZnO heterostructures that exhibit quantum Hall effect. At low temperatures, our nominally non-magnetic heterostructures display an anomalous Hall effect response similar to that of a clean ferromagnetic metal, while keeping a large anomalous Hall effect angle \u03b8_(AHE) \u2248 20\u00b0. Such a behaviour is consistent with Giovannini\u2013Kondo model in which the anomalous Hall effect arises from the skew scattering of electrons by localized paramagnetic centres. Our study unveils a new aspect of many-body interactions in two-dimensional electron systems and shows how the anomalous Hall effect can emerge in a non-magnetic system.", "doi": "10.1038/ncomms14777", "pmcid": "PMC5357314", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2017-03-16", "volume": "8", "pages": "Art. No. 14777" }, { "id": "authors:jcner-q5833", "collection": "authors", "collection_id": "jcner-q5833", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-145517903", "type": "article", "title": "Hall field-induced resistance oscillations in MgZnO/ZnO heterostructures", "author": [ { "family_name": "Shi", "given_name": "Q.", "clpid": "Shi-Q" }, { "family_name": "Zudov", "given_name": "M. A.", "clpid": "Zudov-M-A" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "von Klitzing", "given_name": "K.", "orcid": "0000-0002-1720-7396", "clpid": "von-Klitzing-K" }, { "family_name": "Smet", "given_name": "J.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" } ], "abstract": "We report on nonlinear magnetotransport in a two-dimensional electron gas hosted in a MgZnO/ZnO heterostructure. Upon application of a direct current, we observe pronounced Hall field\u2013induced resistance oscillations (HIRO), which are well known from experiments on high-mobility GaAs/AlGaAs quantum wells. The unique sensitivity of HIRO to the short-range component of the disorder potential allows us to unambiguously establish that the mobility of our MgZnO/ZnO heterostructure is limited by impurities residing within or near the two-dimensional (2D) channel. This demonstration that HIRO can be realized in a system with a much lower mobility, much higher density, and much larger effective mass than in previously studied systems highlights the remarkable universality of the phenomenon and its great promise for use in studies of a wide variety of emerging 2D materials.", "doi": "10.1103/physrevb.95.041411", "issn": "2469-9950", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2017-01-15", "series_number": "4", "volume": "95", "issue": "4", "pages": "Art. No. 041411" }, { "id": "authors:4b8x2-9bw57", "collection": "authors", "collection_id": "4b8x2-9bw57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144732967", "type": "article", "title": "Alloy disorder modulated electron transport at Mg_xZn_(1-x)O/ZnO heterointerface", "author": [ { "family_name": "Vishnuradhan", "given_name": "Aswin", "clpid": "Vishnuradhan-A" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Uchida", "given_name": "M.", "orcid": "0000-0002-0735-8844", "clpid": "Uchida-Masaki" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "High-mobility electron systems in two dimensions have been the platform for realizing many fascinating quantum phenomena at low temperatures. Continuous demand to improve the sample quality has necessitated the investigations of various disorders influencing the quantum transport. Here, we study the effect of short-ranged alloy disorder on the scattering of two-dimensional electron system in Mg_xZn_(1-x)O/ZnO. For this purpose, we employ a modified interface profile consisting of Mg_(0.01)Zn_(0.99)O/ZnO with a thin (2nm) Mg_xZn_(1-x)O interlayer with x ranging from 0.005 to 0.4. This interlayer design allows us to investigate scattering mechanisms at a nearly constant carrier density as the interlayer is found not to significantly affect the carrier density but enhance alloy disorder. While the transport scattering time (\u03c4_(tr)) shows a strong correlation with x, the quantum scattering time (\u03c4_q) remains insensitive to x. The large variation in the \u03c4_(tr)/\u03c4_q ratio (from 16.2 to 1.5 corresponding to x from 0.005 to 0.4) implies a change in the dominant scattering mechanism from long range towards short range with increasing x. The insensitivity of \u03c4q on x indicates the scattering rate is not dominated by the alloy disorder. This implies that other scattering mechanisms, likely unintentional background impurities or remote surface disorders, are dominant in limiting \u03c4_q, and therefore providing a prospect for pursuing ever higher levels in the quality of the two-dimensional electron system in Mg_xZn_(1-x)O/ZnO system.", "doi": "10.1063/1.4974462", "issn": "2158-3226", "publisher": "American Institute of Physics", "publication": "AIP Advances", "publication_date": "2017-01", "series_number": "1", "volume": "7", "issue": "1", "pages": "Art. No. 015029" }, { "id": "authors:9w7kj-z5262", "collection": "authors", "collection_id": "9w7kj-z5262", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144733064", "type": "article", "title": "MgZnO/ZnO heterostructures with electron mobility exceeding 1\u2009\u00d7\u200910\u2076\u2009cm\u00b2/Vs", "author": [ { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Yusuke", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Uchida", "given_name": "Masaki", "orcid": "0000-0002-0735-8844", "clpid": "Uchida-Masaki" }, { "family_name": "Smet", "given_name": "Jurgen H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-Jurgen-H" }, { "family_name": "Arima", "given_name": "Taka-hisa", "orcid": "0000-0002-6959-0454", "clpid": "Arima-Taka-hisa" }, { "family_name": "Tsukazaki", "given_name": "Atsushi", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "Masashi", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "The inherently complex chemical and crystallographic nature of oxide materials has suppressed the purities achievable in laboratory environments, obscuring the rich physical degrees of freedom these systems host. In this manuscript we provide a systematic approach to defect identification and management in oxide molecular beam epitaxy grown MgZnO/ZnO heterostructures which host two-dimensional electron systems. We achieve samples displaying electron mobilities in excess of 1\u2009\u00d7\u200910\u2076\u2009cm\u00b2/Vs. This data set for the MgZnO/ZnO system firmly establishes that the crystalline quality has become comparable to traditional semiconductor materials.", "doi": "10.1038/srep26598", "pmcid": "PMC4882538", "issn": "2045-2322", "publisher": "Nature Publishing Group", "publication": "Scientific Reports", "publication_date": "2016-05-27", "volume": "6", "pages": "Art. No. 26598" }, { "id": "authors:rekg5-5v660", "collection": "authors", "collection_id": "rekg5-5v660", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144733184", "type": "article", "title": "Observation of the quantum Hall effect in \u03b4-doped SrTiO\u2083", "author": [ { "family_name": "Matsubara", "given_name": "Y.", "clpid": "Matsubara-Y" }, { "family_name": "Takahashi", "given_name": "K. S.", "clpid": "Takahashi-K-S" }, { "family_name": "Bahramy", "given_name": "M. S.", "clpid": "Bahramy-M-S" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Tokura", "given_name": "Y.", "clpid": "Tokura-Y" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "The quantum Hall effect is a macroscopic quantum phenomenon in a two-dimensional electron system. The two-dimensional electron system in SrTiO\u2083 has sparked a great deal of interest, mainly because of the strong electron correlation effects expected from the 3d orbitals. Here we report the observation of the quantum Hall effect in a dilute La-doped SrTiO\u2083-two-dimensional electron system, fabricated by metal organic molecular-beam epitaxy. The quantized Hall plateaus are found to be solely stemming from the low Landau levels with even integer-filling factors, \u03bd=4 and 6 without any contribution from odd \u03bd's. For \u03bd=4, the corresponding plateau disappears on decreasing the carrier density. Such peculiar behaviours are proposed to be due to the crossing between the Landau levels originating from the two subbands composed of d orbitals with different effective masses. Our findings pave a way to explore unprecedented quantum phenomena in d-electron systems.", "doi": "10.1038/ncomms11631", "pmcid": "PMC4894966", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2016-05-27", "volume": "7", "pages": "Art. No. 11631" }, { "id": "authors:rs6cw-hjg67", "collection": "authors", "collection_id": "rs6cw-hjg67", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144733296", "type": "article", "title": "Observation of microwave induced resistance and photovoltage oscillations in MgZnO/ZnO heterostructures", "author": [ { "family_name": "K\u00e4rcher", "given_name": "D. F.", "clpid": "K\u00e4rcher-D-F" }, { "family_name": "Shchepetilnikov", "given_name": "A. V.", "clpid": "Shchepetilnikov-A-V" }, { "family_name": "Nefyodov", "given_name": "Yu. A.", "clpid": "Nefyodov-Yu-A" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Dmitriev", "given_name": "I. A.", "clpid": "Dmitriev-I-A" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Dorozhkin", "given_name": "S. I.", "clpid": "Dorozhkin-S-I" }, { "family_name": "Kukushkin", "given_name": "I. V.", "clpid": "Kukushkin-I-V" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "Smet", "given_name": "J. H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" } ], "abstract": "Microwave induced resistance and photovoltage oscillations were investigated in Mg_xZn_(1\u2212x)O/ZnO heterostructures. The physics of these oscillations is controlled significantly by scattering mechanisms, and therefore these experiments were motivated by the recently achieved high quality levels in this material and the apparent dominance of large angle, short-range scattering, which is distinct from the prevailing small angle scattering in state-of-the-art GaAs structures. Within the studied frequency range of 35\u2013120 GHz, up to four oscillations were resolved at 1.4 K temperature, but only in high density samples. This allowed us to extract the value of the effective electron mass m^\u2217 = (0.35 \u00b1 0.01)m\u2080, which is enhanced over the bare band mass, and estimate a local quantum scattering time of about 5 ps.", "doi": "10.1103/physrevb.93.041410", "issn": "2469-9950", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2016-01-15", "series_number": "4", "volume": "93", "issue": "4", "pages": "Art. No. 041410(R)" }, { "id": "authors:zenn1-05k67", "collection": "authors", "collection_id": "zenn1-05k67", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144733416", "type": "article", "title": "Spin-Selective Electron Quantum Transport in Nonmagnetic MgZnO/ZnO Heterostructures", "author": [ { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Bahramy", "given_name": "M.\u2009S.", "clpid": "Bahramy-M-S" }, { "family_name": "Dmitriev", "given_name": "I.\u2009A.", "clpid": "Dmitriev-I-A" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "We report magnetotransport measurements on a high-mobility two-dimensional electron system at the nonmagnetic MgZnO/ZnO heterointerface showing distinct behavior for electrons with spin-up and spin-down orientations. The low-field Shubnikov\u2013de Haas oscillations manifest alternating resistance peak heights which can be attributed to distinct scattering rates for different spin orientations. The tilt-field measurements at a half-integer filling factor reveal that the majority spins show usual diffusive behavior, i.e., peaks with the magnitude proportional to the index of the Landau level at the Fermi energy. By contrast, the minority spins develop \"plateaus\" with the magnitude of dissipative resistivity that is fairly independent of the Landau level index and is of the order of the zero-field resistivity.", "doi": "10.1103/physrevlett.115.197601", "issn": "0031-9007", "publisher": "American Physical Society", "publication": "Physical Review Letters", "publication_date": "2015-11-06", "series_number": "19", "volume": "115", "issue": "19", "pages": "Art. No. 197601" }, { "id": "authors:20hp5-bye92", "collection": "authors", "collection_id": "20hp5-bye92", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144733538", "type": "article", "title": "Electron scattering times in ZnO based polar heterostructures", "author": [ { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Smet", "given_name": "J. H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" }, { "family_name": "Arima", "given_name": "T.", "orcid": "0000-0002-6959-0454", "clpid": "Arima-Taka-hisa" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "The remarkable historic advances experienced in condensed matter physics have been enabled through the continued exploration and proliferation of increasingly richer and cleaner material systems. In this work, we report on the scattering times of charge carriers confined in state-of-the-art MgZnO/ZnO heterostructures displaying electron mobilities in excess of 10\u2076 cm\u00b2/V s. Through an examination of low field quantum oscillations, we obtain the effective mass of charge carriers, along with the transport and quantum scattering times. These times compare favorably with high mobility AlGaAs/GaAs heterostructures, suggesting the quality of MgZnO/ZnO heterostructures now rivals that of traditional semiconductors.", "doi": "10.1063/1.4929381", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2015-08-24", "series_number": "8", "volume": "107", "issue": "8", "pages": "Art. No. 082102" }, { "id": "authors:hhd6k-k2873", "collection": "authors", "collection_id": "hhd6k-k2873", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200403-115230763", "type": "article", "title": "Quantum Hall effect on top and bottom surface states of topological insulator (Bi_(1\u2212x)Sb_x)\u2082Te\u2083 films", "author": [ { "family_name": "Yoshimi", "given_name": "R.", "clpid": "Yoshimi-R" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Takahashi", "given_name": "K. S.", "clpid": "Takahashi-K-S" }, { "family_name": "Checkelsky", "given_name": "J. G.", "clpid": "Checkelsky-J-G" }, { "family_name": "Nagaosa", "given_name": "N.", "clpid": "Nagaosa-N" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "Tokura", "given_name": "Y.", "clpid": "Tokura-Y" } ], "abstract": "The three-dimensional topological insulator is a novel state of matter characterized by two-dimensional metallic Dirac states on its surface. To verify the topological nature of the surface states, Bi-based chalcogenides such as Bi\u2082Se\u2083, Bi\u2082Te\u2083, Sb\u2082Te\u2083 and their combined/mixed compounds have been intensively studied. Here, we report the realization of the quantum Hall effect on the surface Dirac states in (Bi_(1\u2212x)Sb_x)\u2082Te\u2083 films. With electrostatic gate-tuning of the Fermi level in the bulk band gap under magnetic fields, the quantum Hall states with filling factor \u00b11 are resolved. Furthermore, the appearance of a quantum Hall plateau at filling factor zero reflects a pseudo-spin Hall insulator state when the Fermi level is tuned in between the energy levels of the non-degenerate top and bottom surface Dirac points. The observation of the quantum Hall effect in three-dimensional topological insulator films may pave a way toward topological insulator-based electronics.", "doi": "10.1038/ncomms7627", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2015-05", "series_number": "5", "volume": "6", "issue": "5", "pages": "Art. No. 6627" }, { "id": "authors:v9kb5-8x472", "collection": "authors", "collection_id": "v9kb5-8x472", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144733665", "type": "article", "title": "Even-denominator fractional quantum Hall physics in ZnO", "author": [ { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Friess", "given_name": "B.", "clpid": "Friess-B" }, { "family_name": "Zhang", "given_name": "D.", "orcid": "0000-0002-8334-8349", "clpid": "Zhang-Ding" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Smet", "given_name": "J. H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "The fractional quantum Hall (FQH) effect emerges in high-quality two-dimensional electron systems exposed to a magnetic field when the Landau-level filling factor, \u03bd_e, takes on a rational value. Although the overwhelming majority of FQH states have odd-denominator fillings, the physical properties of the rare and fragile even-denominator states are most tantalizing in view of their potential relevance for topological quantum computation. For decades, GaAs has been the preferred host for studying these even-denominator states, where they occur at \u03bd_e = 5/2 and 7/2. Here we report an anomalous series of quantized even-denominator FQH states outside the realm of III\u2013V semiconductors in the MgZnO/ZnO 2DES electron at \u03bd_e = 3/2 and 7/2, with precursor features at 9/2; all while the 5/2 state is absent. The effect in this material occurs concomitantly with tunability of the orbital character of electrons at the chemical potential, thereby realizing a new experimental means for investigating these exotic ground states.", "doi": "10.1038/nphys3259", "issn": "1745-2473", "publisher": "Nature Publishing Group", "publication": "Nature Physics", "publication_date": "2015-04", "series_number": "4", "volume": "11", "issue": "4", "pages": "347-351" }, { "id": "authors:f7c9h-neg08", "collection": "authors", "collection_id": "f7c9h-neg08", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144733764", "type": "article", "title": "Optical probing of MgZnO/ZnO heterointerface confinement potential energy levels", "author": [ { "family_name": "Solovyev", "given_name": "V. V.", "clpid": "Solovyev-V-V" }, { "family_name": "Van'kov", "given_name": "A. B.", "clpid": "Van'kov-A-B" }, { "family_name": "Kukushkin", "given_name": "I. V.", "clpid": "Kukushkin-I-V" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Zhang", "given_name": "D.", "orcid": "0000-0002-8334-8349", "clpid": "Zhang-Ding" }, { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Smet", "given_name": "J. H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "Low-temperature photoluminescence and reflectance measurements were employed to study the optical transitions present in two-dimensional electron systems confined at Mg_xZn_(1\u2013x)O/ZnO heterojunctions. Transitions involving A- and B-holes and electrons from the two lowest subbands formed within the confinement potential are detected. In the studied density range of 2.0\u20136.5\u2009\u00d7\u200910\u00b9\u00b9\u2009cm\u207b\u00b2, the inter-subband splitting is measured and the first excited electron subband is shown to be empty of electrons.", "doi": "10.1063/1.4913313", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2015-02-23", "series_number": "8", "volume": "106", "issue": "8", "pages": "Art. No. 082102" }, { "id": "authors:8c8xy-f1z29", "collection": "authors", "collection_id": "8c8xy-f1z29", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144733869", "type": "article", "title": "Microwave magnetoplasma resonances of two-dimensional electrons in MgZnO/ZnO heterojunctions", "author": [ { "family_name": "Kozlov", "given_name": "V. E.", "clpid": "Kozlov-V-E" }, { "family_name": "Van'kov", "given_name": "A. B.", "clpid": "Van'kov-A-B" }, { "family_name": "Gubarev", "given_name": "S. I.", "clpid": "Gubarev-S-I" }, { "family_name": "Kukushkin", "given_name": "I. V.", "clpid": "Kukushkin-I-V" }, { "family_name": "Solovyev", "given_name": "V. V.", "clpid": "Solovyev-V-V" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "Smet", "given_name": "J. H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" } ], "abstract": "The plasma, magnetoplasma, and edge magnetoplasma excitations were investigated in two-dimensional electron systems hosted at the heterointerface of MgZnO/ZnO structures using optical detection of resonant microwave absorption. The magnetodispersion of the plasma excitations allowed the extraction of the electron effective mass. It was found to exhibit a surprisingly large dependence on the electron density, which is difficult to account for just from nonparabolicity effects.", "doi": "10.1103/physrevb.91.085304", "issn": "1098-0121", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2015-02-15", "series_number": "8", "volume": "91", "issue": "8", "pages": "Art. No. 085304" }, { "id": "authors:ggjw0-sj046", "collection": "authors", "collection_id": "ggjw0-sj046", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144733977", "type": "article", "title": "Calibration and control of in-plane Mg doping distribution in Mg_xZn_(1\u2212x)O/ZnO heterostructures grown by molecular beam epitaxy", "author": [ { "family_name": "Uchida", "given_name": "Masaki", "orcid": "0000-0002-0735-8844", "clpid": "Uchida-Masaki" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Segawa", "given_name": "Yusaburo", "clpid": "Segawa-Yusaburo" }, { "family_name": "Kozuka", "given_name": "Yusuke", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "Atsushi", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "Masashi", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "The in-plane Mg doping distribution in molecular beam epitaxy grown Mg_xZn_(1\u2212x)O/ZnO heterostructures is mapped by low-temperature photoluminescence measurements in an effort to evaluate and control the resultant inhomogeneity formed during the growth process. In an unrotated sample, the independent configuration effects of the O\u2083 and Mg source cells are clearly demonstrated in a composition spread due to flux gradients, while this inhomogeneity is suppressed by sample rotation during the growth. The present mapping results provide an important means for investigating improved doping regimes with the aim of enhancing the quality of quantum transport observable at the Mg_xZn_(1\u2212x)O/ZnO heterointerface.", "doi": "10.7567/jjap.54.028004", "issn": "0021-4922", "publisher": "Japan Society of Applied Physics", "publication": "Japanese Journal of Applied Physics", "publication_date": "2015-02", "series_number": "2", "volume": "54", "issue": "2", "pages": "Art. No. 028004" }, { "id": "authors:575ad-5vb82", "collection": "authors", "collection_id": "575ad-5vb82", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200403-115230571", "type": "article", "title": "Polarization-dependent Landau level crossing in a two-dimensional electron system in a MgZnO/ZnO heterostructure", "author": [ { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "We report electrical transport measurements in a tilted magnetic field on a high-mobility two-dimensional electron system (2DES) confined at the MgZnO/ZnO heterointerface. The observation of multiple crossing events of spin-resolved Landau levels (LLs) enables the mapping of the sequence of electronic states. We further measure the renormalization of electron spin susceptibility at zero field and the susceptibility dependence on the electron spin polarization. The latter manifests the deviation from the Pauli spin susceptibility. As a result, the crossing of spin-resolved LLs shifts to smaller tilt angles and the first Landau level coincidence event is absent even when the magnetic field has only a component perpendicular to the 2DES plane.", "doi": "10.1103/physrevb.90.245303", "issn": "1098-0121", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2014-12-15", "series_number": "24", "volume": "90", "issue": "24", "pages": "Art. No. 245303" }, { "id": "authors:g3ecf-tk597", "collection": "authors", "collection_id": "g3ecf-tk597", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200403-115230885", "type": "article", "title": "Trajectory of the anomalous Hall effect towards the quantized state in a ferromagnetic topological insulator", "author": [ { "family_name": "Checkelsky", "given_name": "J. G.", "clpid": "Checkelsky-J-G" }, { "family_name": "Yoshimi", "given_name": "R.", "clpid": "Yoshimi-R" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Takahashi", "given_name": "K. S.", "clpid": "Takahashi-K-S" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "Tokura", "given_name": "Y.", "clpid": "Tokura-Y" } ], "abstract": "Topological insulators are bulk electronic insulators with symmetry-protected gapless modes on their surfaces. Breaking time-reversal symmetry in these systems via ferromagnetism induces a gapped state characterized by a zero magnetic field quantized Hall response\u2014the quantum anomalous Hall (QAH) state. A key question that has remained experimentally unexplored is the relationship of this new type of quantum Hall (QH) state with the previously known orbitally driven QH states. Here, we show experimentally that a ferromagnetic topological insulator exhibiting the QAH state is well described by the global phase diagram of the QH effect. By mapping the conductivity tensor in the vicinity of the QAH phase, we find evidence for quantum criticality and delocalization behaviour that can quantitatively be described by the renormalization group properties of the QH ground state. This result demonstrates that this QAH state can be understood within the context of the law of corresponding states that governs the QH state.", "doi": "10.1038/nphys3053", "issn": "1745-2473", "publisher": "Nature Publishing Group", "publication": "Nature Physics", "publication_date": "2014-10", "series_number": "10", "volume": "10", "issue": "10", "pages": "731-736" }, { "id": "authors:jbdsj-hc953", "collection": "authors", "collection_id": "jbdsj-hc953", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144734077", "type": "article", "title": "Air-gap gating of MgZnO/ZnO heterostructures", "author": [ { "family_name": "Tambo", "given_name": "T.", "clpid": "Tambo-T" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "The adaptation of \"air-gap\" dielectric based field-effect transistor technology to controlling the MgZnO/ZnO heterointerface confined two-dimensional electron system (2DES) is reported. We find it possible to tune the charge density of the 2DES via a gate electrode spatially separated from the heterostructure surface by a distance of 5\u2009\u03bcm. Under static gating, the observation of the quantum Hall effect suggests that the charge carrier density remains homogeneous, with the 2DES in the 3\u2009mm square sample the sole conductor. The availability of this technology enables the exploration of the charge carrier density degree of freedom in the pristine sample limit.", "doi": "10.1063/1.4894155", "issn": "0021-8979", "publisher": "American Institute of Physics", "publication": "Journal of Applied Physics", "publication_date": "2014-08-28", "series_number": "8", "volume": "116", "issue": "8", "pages": "Art. No. 084310" }, { "id": "authors:3mfak-1cw83", "collection": "authors", "collection_id": "3mfak-1cw83", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144734163", "type": "article", "title": "Spontaneous polarization driven Mg concentration profile reconstruction in MgZnO/ZnO heterostructures", "author": [ { "family_name": "Imasaka", "given_name": "K.", "clpid": "Imasaka-K" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "Atomic reconstruction at the interface of MgZnO and ZnO in molecular beam epitaxy grown heterostructures is investigated. Using secondary ion mass spectroscopy, we experimentally find that Mg atomic reconstruction depends on the polarity of the interface; it is not observed in n-type interfaces (MgZnO on Zn-polar ZnO) owing to electron accumulation, while in p-type interfaces (ZnO on Zn-polar MgZnO), Mg drastically redistributes into the ZnO layer. Combined with self-consistent calculation of band profiles and carrier distributions, we reveal that the observed Mg reconstruction is not due to thermal diffusion but consequences in order to avoid hole accumulation. This tendency implies inherent significant asymmetry of energy scales of atomic and electronic reconstructions between n-type and p-type interfaces.", "doi": "10.1063/1.4884383", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2014-06-16", "series_number": "24", "volume": "104", "issue": "24", "pages": "Art. No. 242112" }, { "id": "authors:8v1wr-my224", "collection": "authors", "collection_id": "8v1wr-my224", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200403-115230987", "type": "article", "title": "Enhanced quantum oscillatory magnetization and nonequilibrium currents in an interacting two-dimensional electron system in MgZnO/ZnO with repulsive scatterers", "author": [ { "family_name": "Brasse", "given_name": "M.", "clpid": "Brasse-M" }, { "family_name": "Sauther", "given_name": "S. M.", "clpid": "Sauther-S-M" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Heyn", "given_name": "Ch.", "clpid": "Heyn-Ch" }, { "family_name": "Wilde", "given_name": "M. A.", "clpid": "Wide-M-A" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "Grundler", "given_name": "D.", "clpid": "Grundler-D" } ], "abstract": "Torque magnetometry at low temperature and in high magnetic fields B is performed on MgZnO/ZnO heterostructures incorporating high-mobility two-dimensional electron systems. We find a sawtoothlike quantum oscillatory magnetization M(B), i.e., the de Haas-van Alphen (dHvA) effect. At the same time, nonequilibrium currents and unexpected spikelike overshoots in M are observed which allow us to identify the microscopic nature and density of the residual disorder. The acceptorlike scatterers give rise to a magnetic thaw down effect which enhances the dHvA amplitude beyond the electron-electron interaction effects being present in the MgZnO/ZnO heterostructures.", "doi": "10.1103/physrevb.89.075307", "issn": "1098-0121", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2014-02-15", "series_number": "7", "volume": "89", "issue": "7", "pages": "Art. No. 075307" }, { "id": "authors:d3ga5-t2280", "collection": "authors", "collection_id": "d3ga5-t2280", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144734256", "type": "article", "title": "Observation of plasma and magnetoplasma resonances of two-dimensional electrons in a single MgZnO/ZnO heterojunction", "author": [ { "family_name": "Kozlov", "given_name": "V. E.", "clpid": "Kozlov-V-E" }, { "family_name": "Van'kov", "given_name": "A. B.", "clpid": "Van'kov-A-B" }, { "family_name": "Gubarev", "given_name": "S. I.", "clpid": "Gubarev-S-I" }, { "family_name": "Kukushkin", "given_name": "I. V.", "clpid": "Kukushkin-I-V" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "Smet", "given_name": "J. H.", "orcid": "0000-0002-4719-8873", "clpid": "Smet-J-H" } ], "abstract": "The magnetoluminescence of the two-dimensional electron system in a single Mg_x Zn_(1\u2212x)O/ZnO heterojunction (x = 0.02) at a temperature of 0.3 K in magnetic fields up to 14 T has been studied. The concentration of two-dimensional electrons in the structure under study has been determined from the oscillations of the luminescence intensity as a function of the magnetic field. The value thus obtained is close to the one derived from transport measurements. The resonance corresponding to plasma excitations of two-dimensional electrons has been observed using optical detection of microwave absorption. In a magnetic field, the lower branch of magnetoplasma excitations, which corresponds to the propagation of edge magnetoplasmons in a structure with nearly square geometry, has been observed and investigated.", "doi": "10.1134/s0021364013170074", "issn": "0021-3640", "publisher": "Pleiades Publishing Ltd", "publication": "JETP Letters", "publication_date": "2013-10", "series_number": "4", "volume": "98", "issue": "4", "pages": "223-226" }, { "id": "authors:d33m9-mw557", "collection": "authors", "collection_id": "d33m9-mw557", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144734366", "type": "article", "title": "Rashba spin-orbit interaction in a Mg_xZn_(1\u2212x)O/ZnO two-dimensional electron gas studied by electrically detected electron spin resonance", "author": [ { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Teraoka", "given_name": "S.", "clpid": "Teraoka-S" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Oiwa", "given_name": "A.", "clpid": "Oiwa-A" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Tarucha", "given_name": "S.", "clpid": "Tarucha-S" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "We report the experimental determination of Rashba spin-orbit interaction (SOI) strength in two-dimensional electrons in a MgZnO/ZnO heterostructure using electrically detected electron spin resonance. The Rashba parameter is determined to be \n7.0 \u00d7 10\u207b\u00b9\u2074 eV\u2009m, which is the second smallest value among prevalent semiconductor heterostructures, following Si/SiGe. A long transverse spin relaxation time was derived to show a maximum value of 27 ns, owing to weak SOI. Our study demonstrates that the ZnO heterostructure is a promising candidate for spintronic devices utilizing long spin coherence.", "doi": "10.1103/physrevb.87.205411", "issn": "1098-0121", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2013-05-15", "series_number": "20", "volume": "87", "issue": "20", "pages": "Art. No. 205411" }, { "id": "authors:sp9yg-3xv40", "collection": "authors", "collection_id": "sp9yg-3xv40", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144734477", "type": "article", "title": "Correlation-Enhanced Effective Mass of Two-Dimensional Electrons in Mg_xZn_(1\u2212x)O/ZnO Heterostructures", "author": [ { "family_name": "Kasahara", "given_name": "Y.", "clpid": "Kasahara-Y" }, { "family_name": "Oshima", "given_name": "Y.", "clpid": "Oshima-Y" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" }, { "family_name": "Iwasa", "given_name": "Y.", "clpid": "Iwasa-Y" } ], "abstract": "We performed combined magnetotransport and cyclotron resonance experiments on two-dimensional electron systems confined in the \nMg_xZn_(1\u2212x)O/ZnO heterostructures over a wide range of carrier densities, from 1.9 to 12 \u00d7 10\u00b9\u00b9 cm\u207b\u00b2 (3.5 \u2272 r_s \u2272 10, where r_s is the Wigner-Seitz radius). As the carrier density was reduced, the transport mass m*\u2217_(tr) was strongly enhanced. In marked contrast, the effective masses determined from the cyclotron resonance \nm^\u2217_(CR) were found to be independent of the carrier density and as large as the bulk effective mass. The large enhancement of m^\u2217_(tr), which exceeds m^\u2217_(CR) by \u223c60%, at the lowest carrier density with r_s \u223c 10 is purely attributed to the strong electron correlation.", "doi": "10.1103/physrevlett.109.246401", "issn": "0031-9007", "publisher": "American Physical Society", "publication": "Physical Review Letters", "publication_date": "2012-12-14", "series_number": "24", "volume": "109", "issue": "24", "pages": "Art. No. 246401" }, { "id": "authors:s6p61-t8665", "collection": "authors", "collection_id": "s6p61-t8665", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200403-115231081", "type": "article", "title": "Precise calibration of Mg concentration in Mg_xZn_(1\u2212x)O thin films grown on ZnO substrates", "author": [ { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Segawa", "given_name": "Y.", "clpid": "Segawa-Yusaburo" }, { "family_name": "Makino", "given_name": "T.", "clpid": "Makino-T" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "The growth techniques for Mg_xZn_(1\u2212x)O thin films have advanced at a rapid pace in recent years, enabling the application of this material to a wide range of optical and electrical applications. In designing structures and optimizing device performances, it is crucial that the Mg content of the alloy be controllable and precisely determined. In this study, we have established laboratory-based methods to determine the Mg content of Mg_xZn_(1\u2212x)O thin films grown on ZnO substrates, ranging from the solubility limit of x\u2009\u223c\u20090.4 to the dilute limit of x\u2009<\u20090.01. For the absolute determination of Mg content, Rutherford backscattering spectroscopy is used for the high Mg region above x\u2009=\u20090.14, while secondary ion mass spectroscopy is employed to quantify low Mg content. As a lab-based method to determine the Mg content, c-axis length is measured by x-ray diffraction and is well associated with Mg content. The interpolation enables the determination of Mg content to x\u2009=\u20090.023, where the peak from the ZnO substrate overlaps the Mg_xZn_(1\u2212x)O peak in standard laboratory equipment, and thus limits quantitative determination. At dilute Mg contents below x\u2009=\u20090.023, the localized exciton peak energy of the Mg_xZn_(1\u2212x)O films as measured by photoluminescence is found to show a linear Mg content dependence, which is well resolved from the free exciton peak of ZnO substrate down to x\u2009=\u20090.0043. Our results demonstrate that x-ray diffraction and photoluminescence in combination are appropriate methods to determine Mg content in a wide Mg range from x\u2009=\u20090.004 to 0.40 in a laboratory environment.", "doi": "10.1063/1.4748306", "issn": "0021-8979", "publisher": "American Institute of Physics", "publication": "Journal of Applied Physics", "publication_date": "2012-08-15", "series_number": "4", "volume": "112", "issue": "4", "pages": "Art. No. 043515" }, { "id": "authors:ttvm0-vph86", "collection": "authors", "collection_id": "ttvm0-vph86", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200403-115231169", "type": "article", "title": "Temperature-Dependent Magnetotransport around \u03bd=1/2 in ZnO Heterostructures", "author": [ { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Onoda", "given_name": "M.", "clpid": "Onoda-M" }, { "family_name": "Aoki", "given_name": "H.", "clpid": "Aoki-H" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "The sequence of prominent fractional quantum Hall states up to \u03bd = 5/11 around \u03bd = 1/2 in a high-mobility two-dimensional electron system confined at oxide heterointerface (ZnO) is analyzed in terms of the composite fermion model. The temperature dependence of R_(xx) oscillations around \u03bd = 1/2 yields an estimation of the composite fermion effective mass, which increases linearly with the magnetic field. This mass is of similar value to an enhanced electron effective mass, which in itself arises from strong electron interaction. The energy gaps of fractional states and the temperature dependence of R_(xx) at \u03bd = 1/2 point to large residual interactions between composite fermions.", "doi": "10.1103/physrevlett.108.186803", "issn": "0031-9007", "publisher": "American Physical Society", "publication": "Physical Review Letters", "publication_date": "2012-05-04", "series_number": "18", "volume": "108", "issue": "18", "pages": "Art. No. 186803" }, { "id": "authors:5hxq5-be819", "collection": "authors", "collection_id": "5hxq5-be819", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200402-144734572", "type": "article", "title": "Single-valley quantum Hall ferromagnet in a dilute Mg_xZn_(1\u2212x)O/ZnO strongly correlated two-dimensional electron system", "author": [ { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Bell", "given_name": "C.", "clpid": "Bell-C" }, { "family_name": "Kim", "given_name": "M.", "clpid": "Kim-M" }, { "family_name": "Hikita", "given_name": "Y.", "clpid": "Hikita-Y" }, { "family_name": "Hwang", "given_name": "H. Y.", "clpid": "Hwang-H-Y" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "We investigate the spin susceptibility (g^\u2217m^\u2217) of dilute two-dimensional (2D) electrons confined at the Mg_xZn_(1\u2212x)O/ZnO heterointerface. Magnetotransport measurements show a four-fold enhancement of g^\u2217m^\u2217, dominated by the increase in the Land\u00e9 \ng-factor. The g-factor enhancement leads to a ferromagnetic instability of the electron gas as evidenced by sharp resistance spikes. At high magnetic field, the large g^\u2217m^\u2217 leads to full spin polarization, where we found sudden increase in resistance around the filling factors of half-integer, accompanied by complete disappearance of fractional quantum Hall (QH) states. Along with its large effective mass and the high electron mobility, our result indicates that the ZnO 2D system is ideal for investigating the effect of electron correlations in the QH regime.", "doi": "10.1103/physrevb.85.075302", "issn": "1098-0121", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2012-02-15", "series_number": "7", "volume": "85", "issue": "7", "pages": "Art. No. 075302" }, { "id": "authors:29fej-27t76", "collection": "authors", "collection_id": "29fej-27t76", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200403-115231482", "type": "article", "title": "Magnesium Doping Controlled Density and Mobility of Two-Dimensional Electron Gas in Mg_xZn_(1-x)O/ZnO Heterostructures", "author": [ { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Maryenko", "given_name": "Denis", "clpid": "Maryenko-D" }, { "family_name": "Kozuka", "given_name": "Yusuke", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "Atsushi", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Kawasaki", "given_name": "Masashi", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "The magnesium content in Mg_xZn_(1-x)O/ZnO heterostructures grown by molecular beam epitaxy enables the careful control of the carrier density of the two-dimensional electron system down to 5.6\u00d710\u00b9\u2079 cm\u207b\u00b2 while retaining a mobility of 200,000 cm\u00b2 V\u207b\u00b9 s\u207b\u00b9 when pursuing magnesium concentrations as low as x = 0.0038. By selecting an optimum magnesium content (x~0.01), the mobility is enhanced to over 700,000 cm\u00b2 V\u207b\u00b9 s\u207b\u00b9 due to reduced impurity levels associated with the use of pure distilled ozone and avoiding interface roughness scattering. This control technique allows access to the coherent transport region with strong electron\u2013electron interaction.", "doi": "10.1143/apex.4.091101", "issn": "1882-0778", "publisher": "Japan Society of Applied Physics", "publication": "Applied Physics Express", "publication_date": "2011-09", "series_number": "9", "volume": "4", "issue": "9", "pages": "Art. No. 091101" }, { "id": "authors:ym1er-bxk94", "collection": "authors", "collection_id": "ym1er-bxk94", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200403-115231264", "type": "article", "title": "Insulating phase of a two-dimensional electron gas in Mg_xZn_(1\u2212x)O/ZnO heterostructures below \u03bd = 1/3", "author": [ { "family_name": "Kozuka", "given_name": "Y.", "orcid": "0000-0001-7674-600X", "clpid": "Kozuka-Yusuke" }, { "family_name": "Tsukazaki", "given_name": "A.", "orcid": "0000-0003-0251-063X", "clpid": "Tsukazaki-Atsushi" }, { "family_name": "Maryenko", "given_name": "D.", "clpid": "Maryenko-D" }, { "family_name": "Falson", "given_name": "J.", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Akasaka", "given_name": "S.", "clpid": "Akasaka-S" }, { "family_name": "Nakahara", "given_name": "K.", "clpid": "Nakahara-K" }, { "family_name": "Nakamura", "given_name": "S.", "clpid": "Nakamura-Shin" }, { "family_name": "Awaji", "given_name": "S.", "clpid": "Awaji-S" }, { "family_name": "Ueno", "given_name": "K.", "clpid": "Ueno-K" }, { "family_name": "Kawasaki", "given_name": "M.", "orcid": "0000-0001-6397-4812", "clpid": "Kawasaki-Masashi" } ], "abstract": "We report magnetotransport properties of a two-dimensional electron gas confined at MgZnO/ZnO heterointerface in a high magnetic field up to 26 T. High electron mobility and low charge carrier density enabled the observation of the fractional quantum Hall state \u03bd = 1/3. For an even lower charge carrier density, we observe a transition from quantum Hall liquid to an insulator below the filling factor 1/3. Because of the large electron effective mass in ZnO, we suggest the MgZnO/ZnO heterostructures to be a prototype system for highly correlated quantum Hall physics.", "doi": "10.1103/physrevb.84.033304", "issn": "1098-0121", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2011-07-15", "series_number": "3", "volume": "84", "issue": "3", "pages": "Art. No. 033304" } ]