Can strong repulsive interactions be shown to give rise to pairing in a controlled way? We find that for a single flavor-polarized band, there is a small expansion parameter in the low density limit, once the Bloch wave-function form factor is taken into account. A perturbative expansion is possible, even if the interaction is much stronger than the Fermi energy \ud835\udf00\ud835\udc39. As a matter of principle, our work shows analytically how strong pairing can emerge from strong repulsion. We illustrate our method with two examples: a two-dimensional Dirac model and a one-dimensional tight-binding model with two orbitals. In the latter case, using density matrix renormalization group, we show that the analytical theory indeed guided us to discover the parameter regime where \ud835\udc5d-wave pairing with order-1 strength is dominant.
", "doi": "10.1103/yw2c-qyj1", "issn": "2469-9950", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2026-03-02", "series_number": "10", "volume": "113", "issue": "10", "pages": "104501" }, { "id": "authors:219sz-ek646", "collection": "authors", "collection_id": "219sz-ek646", "cite_using_url": "https://authors.library.caltech.edu/records/219sz-ek646", "type": "article", "title": "Probing quantum spin liquids with a quantum twisting microscope", "author": [ { "family_name": "Peri", "given_name": "Valerio", "orcid": "0000-0002-0727-3808", "clpid": "Peri-Valerio" }, { "family_name": "Ilani", "given_name": "Shahal", "orcid": "0000-0001-8589-7723", "clpid": "Ilani-Shahal" }, { "family_name": "Lee", "given_name": "Patrick A.", "orcid": "0000-0001-7809-8157", "clpid": "Lee-Patrick-A" }, { "family_name": "Refael", "given_name": "Gil" } ], "abstract": "The experimental characterization of quantum spin liquids poses significant challenges due to the absence of long-range magnetic order, even at absolute zero temperature. The identification of these states of matter often relies on the analysis of their excitations. In this paper, we propose a method for detecting the signatures of the fractionalized excitations in quantum spin liquids using a tunneling spectroscopy setup. Inspired by the recent development of the quantum twisting microscope, we consider a planar tunneling junction, in which a candidate quantum spin-liquid material is placed between two graphene layers. By tuning the relative twist angle and voltage bias between the leads, we can extract the dynamical spin structure factor of the tunneling barrier with momentum and energy resolution. Our proposal presents a promising tool for experimentally characterizing quantum spin liquids in two-dimensional materials.
", "doi": "10.1103/physrevb.109.035127", "issn": "2469-9950", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2024-01-15", "series_number": "3", "volume": "109", "issue": "3", "pages": "035127" }, { "id": "authors:q6zf6-h5c46", "collection": "authors", "collection_id": "q6zf6-h5c46", "cite_using_url": "https://authors.library.caltech.edu/records/q6zf6-h5c46", "type": "article", "title": "Detection of collective modes in unconventional superconductors using tunneling spectroscopy", "author": [ { "family_name": "Lee", "given_name": "Patrick A.", "clpid": "Lee-Patrick-A" }, { "family_name": "Steiner", "given_name": "Jacob F.", "orcid": "0000-0002-2649-9554", "clpid": "Steiner-Jacob-F" } ], "abstract": "We propose using tunneling spectroscopy with a superconducting electrode to probe the collective modes of unconventional superconductors. The modes are predicted to appear as peaks in dI/dV at voltages given by eV = \u03c9\u1d62/2 where \u03c9\u1d62 denotes the mode frequencies. This may prove to be a powerful tool to investigate the pairing symmetry of unconventional superconductors. The peaks associated with the collective modes appear at fourth order in the single-particle tunneling-matrix element. At the same fourth order, multiple Andreev reflection (MAR) leads to peaks at voltage equal to the energy gaps, which, in BCS superconductors, coincides with the expected position of the amplitude (Higgs) mode. The peaks stemming from the collective modes of unconventional superconductors do not suffer from this coincidence. For scanning tunneling microscopes, we estimate that the magnitude of the collective mode contribution is smaller than the MAR contribution by the ratio of the energy gap to the Fermi energy. Moreover, there is no access to the mode dispersion. Conversely, for planar tunnel junctions the collective mode peak is expected to dominate over the MAR peak, and the mode dispersion can be measured. We discuss systems where the search for such collective modes is promising.
", "doi": "10.1103/physrevb.108.174503", "issn": "2469-9950", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2023-11-01", "series_number": "17", "volume": "108", "issue": "17", "pages": "174503" }, { "id": "authors:9w247-4s422", "collection": "authors", "collection_id": "9w247-4s422", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201111-082624574", "type": "article", "title": "A continuous metal-insulator transition driven by spin correlations", "author": [ { "family_name": "Feng", "given_name": "Yejun", "orcid": "0000-0003-3667-056X", "clpid": "Feng-Yejun" }, { "family_name": "Wang", "given_name": "Yishu", "orcid": "0000-0003-1259-8073", "clpid": "Wang-Yishu" }, { "family_name": "Silevitch", "given_name": "D. M.", "orcid": "0000-0002-6347-3513", "clpid": "Silevitch-D-M" }, { "family_name": "Cooper", "given_name": "S. E.", "clpid": "Cooper-S-E" }, { "family_name": "Mandrus", "given_name": "D.", "orcid": "0000-0003-3616-7104", "clpid": "Mandrus-David" }, { "family_name": "Lee", "given_name": "Patrick A.", "clpid": "Lee-Patrick-A" }, { "family_name": "Rosenbaum", "given_name": "T. F.", "orcid": "0009-0008-6152-666X", "clpid": "Rosenbaum-T-F" } ], "abstract": "While Mott insulators induced by Coulomb interactions are a well-recognized class of metal-insulator transitions, insulators purely driven by spin correlations are much less common, as the reduced energy scale often invites competition from other degrees of freedom. Here, we demonstrate a clean example of a spin-correlation-driven metal-insulator transition in the all-in-all-out pyrochlore antiferromagnet Cd\u2082Os\u2082O\u2087, where the lattice symmetry is preserved by the antiferromagnetism. After the antisymmetric linear magnetoresistance from conductive, ferromagnetic domain walls is removed experimentally, the bulk Hall coefficient reveals four Fermi surfaces of both electron and hole types, sequentially departing the Fermi level with decreasing temperature below the N\u00e9el temperature, T_N\u2009=\u2009227 K. In Cd\u2082Os\u2082O\u2087, the charge gap of a continuous metal-insulator transition opens only at T\u2009~\u200910\u2009K\u2009<<\u2009T_N. The insulating mechanism parallels the Slater picture, but without a folded Brillouin zone, and contrasts sharply with Mott insulators and spin density waves, where the electronic gap opens above and at T_N, respectively.", "doi": "10.1038/s41467-021-23039-6", "pmcid": "PMC8119431", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2021-05-13", "volume": "12", "pages": "Art. No. 2779" }, { "id": "authors:gxma1-b2m80", "collection": "authors", "collection_id": "gxma1-b2m80", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210421-103423569", "type": "article", "title": "Topological superconductivity in nanowires proximate to a diffusive superconductor\u2013magnetic-insulator bilayer", "author": [ { "family_name": "Khindanov", "given_name": "Aleksei", "orcid": "0000-0003-4101-0259", "clpid": "Khindanov-Aleksei" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Lee", "given_name": "Patrick", "clpid": "Lee-Patrick-A" }, { "family_name": "Cole", "given_name": "William S.", "clpid": "Cole-William-S" }, { "family_name": "Antipov", "given_name": "Andrey E.", "orcid": "0000-0002-4987-7183", "clpid": "Antipov-Andrey-E" } ], "abstract": "We study semiconductor nanowires coupled to a bilayer of a disordered superconductor and a magnetic insulator, motivated by recent experiments reporting possible Majorana-zero-mode signatures in related architectures. Specifically, we pursue a quasiclassical Usadel equation approach that treats superconductivity in the bilayer self-consistently in the presence of spin-orbit scattering, magnetic-impurity scattering, and Zeeman splitting induced by both the magnetic insulator and a supplemental applied field. Within this framework we explore prospects for engineering topological superconductivity in a nanowire proximate to the bilayer. We find that a magnetic-insulator-induced Zeeman splitting, mediated through the superconductor alone, cannot induce a topological phase since the destruction of superconductivity (i.e., Clogston limit) preempts the required regime in which the nanowire's Zeeman energy exceeds the induced pairing strength. However, this Zeeman splitting does reduce the critical applied field needed to access the topological phase transition, with fields antiparallel to the magnetization of the magnetic insulator having an optimal effect. Finally, we show that magnetic-impurity scattering degrades the topological phase, and spin-orbit scattering, if present in the superconductor, pushes the Clogston limit to higher fields yet simultaneously increases the critical applied field strength.", "doi": "10.1103/physrevb.103.134506", "issn": "2469-9950", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2021-04-01", "series_number": "13", "volume": "103", "issue": "13", "pages": "Art. No. 134506" }, { "id": "authors:r6nmj-zpq39", "collection": "authors", "collection_id": "r6nmj-zpq39", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190624-074905872", "type": "article", "title": "Antisymmetric linear magnetoresistance and the planar Hall effect", "author": [ { "family_name": "Wang", "given_name": "Yishu", "orcid": "0000-0003-1259-8073", "clpid": "Wang-Yishu" }, { "family_name": "Lee", "given_name": "Patrick A.", "clpid": "Lee-Patrick-A" }, { "family_name": "Silevitch", "given_name": "D. M.", "orcid": "0000-0002-6347-3513", "clpid": "Silevitch-D-M" }, { "family_name": "G\u00f3mez", "given_name": "F.", "clpid": "G\u00f3mez-F" }, { "family_name": "Cooper", "given_name": "S. E.", "clpid": "Cooper-S-E" }, { "family_name": "Ren", "given_name": "Y.", "clpid": "Ren-Y" }, { "family_name": "Yan", "given_name": "J.-Q.", "orcid": "0000-0001-6625-4706", "clpid": "Yan-Jiaqiang" }, { "family_name": "Mandrus", "given_name": "D.", "orcid": "0000-0003-3616-7104", "clpid": "Mandrus-D" }, { "family_name": "Rosenbaum", "given_name": "T. F.", "orcid": "0009-0008-6152-666X", "clpid": "Rosenbaum-T-F" }, { "family_name": "Feng", "given_name": "Yejun", "orcid": "0000-0003-3667-056X", "clpid": "Feng-Yejun" } ], "abstract": "The phenomena of antisymmetric magnetoresistance and the planar Hall effect are deeply entwined with ferromagnetism. The intrinsic magnetization of the ordered state permits these unusual and rarely observed manifestations of Onsager's theorem when time reversal symmetry is broken at zero applied field. Here we study two classes of ferromagnetic materials, rare-earth magnets with high intrinsic coercivity and antiferromagnetic pyrochlores with strongly-pinned ferromagnetic domain walls, which both exhibit antisymmetric magnetoresistive behavior. By mapping out the peculiar angular variation of the antisymmetric galvanomagnetic response with respect to the relative alignments of the magnetization, magnetic field, and electrical current, we experimentally distinguish two distinct underlying microscopic mechanisms: namely, spin-dependent scattering of a Zeeman-shifted Fermi surface and anomalous electron velocities. Our work demonstrates that the anomalous electron velocity physics typically associated with the anomalous Hall effect is prevalent beyond the \u03c1_(xy)(H_z) channel, and should be understood as a part of the general galvanomagnetic behavior.", "doi": "10.1038/s41467-019-14057-6", "pmcid": "PMC6954222", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2020-01-10", "volume": "11", "pages": "Art. No. 216" } ]