[
{
"id": "authors:v8jaj-j2q54",
"collection": "authors",
"collection_id": "v8jaj-j2q54",
"cite_using_url": "https://authors.library.caltech.edu/records/v8jaj-j2q54",
"type": "article",
"title": "Correlated terahertz phonon\u2013ion interactions control ion conduction in a solid electrolyte",
"author": [
{
"family_name": "Pham",
"given_name": "Kim H.",
"orcid": "0000-0003-4053-6363",
"clpid": "Pham-Kim-H"
},
{
"family_name": "Gordiz",
"given_name": "Kiarash",
"orcid": "0000-0001-5297-661X"
},
{
"family_name": "Spear",
"given_name": "Natan A.",
"orcid": "0000-0001-7377-5630",
"clpid": "Spear-Natan-A"
},
{
"family_name": "Lin",
"given_name": "Amy K.",
"orcid": "0000-0001-9166-6358",
"clpid": "Lin-Amy-K"
},
{
"family_name": "Michelsen",
"given_name": "Jonathan M.",
"clpid": "Michelsen-Jonathan-M"
},
{
"family_name": "Liu",
"given_name": "Hanzhe",
"orcid": "0000-0001-9001-725X",
"clpid": "Liu-Hanzhe"
},
{
"family_name": "Vivona",
"given_name": "Daniele",
"orcid": "0000-0002-1992-0750"
},
{
"family_name": "Blake",
"given_name": "Geoffrey A.",
"orcid": "0000-0003-0787-1610",
"clpid": "Blake-G-A"
},
{
"family_name": "Shao-Horn",
"given_name": "Yang",
"orcid": "0000-0001-8714-2121"
},
{
"family_name": "Henry",
"given_name": "Asegun",
"orcid": "0000-0002-9097-4882"
},
{
"family_name": "See",
"given_name": "Kimberly A.",
"orcid": "0000-0002-0133-9693",
"clpid": "See-Kimberly"
},
{
"family_name": "Cushing",
"given_name": "Scott K.",
"orcid": "0000-0003-3538-2259",
"clpid": "Cushing-S-K"
}
],
"abstract": "\n
Ionic conduction in solids that exceeds 1 mS cm−1 is predicted to involve coupled phonon–ion interactions in the crystal lattice. Here, we use theory and experiment to measure the possible contribution of coupled phonon–ion hopping modes which enhance Li+ migration in Li0.5La0.5TiO3 (LLTO). The ab initio calculations predict that the targeted excitation of individual TiO6 rocking modes greatly increases the Li+ jump rate as compared to the excitation of vibrational modes associated with heating. Experimentally, coherently driving TiO6 rocking modes via terahertz (THz) illumination leads to a ten-fold decrease in the differential impedance compared to the excitation of acoustic and optical phonons. Additionally, we differentiate the ultrafast responses of LLTO due to ultrafast heating and THz-range vibrations using laser-driven spectroscopy (LUIS), finding a unique long-lived response for the THz-range excitation. These findings provide new insights into coupled ion migration mechanisms, indicating the important role of THz-range coupled phonon–ion hopping modes in enabling fast ion conduction at room temperature.
\n
\n
Ultrafast small-polaron formation profoundly shapes the electronic and catalytic behaviour of transition metal oxides (TMOs). Despite its significance, spectroscopic investigations of photoexcited polaron hopping in TMOs have been scarcely explored. Here, we present the first optical spectroscopic observation of photoexcited small-polaron hopping across the first-row TMOs, using femtosecond transient absorption spectroscopy. This polaronic feature rises within 500 fs as Drude-type absorption converts to localized, polaronic absorption. Fitting with a small-polaron optical conductivity model yields polaron relaxation energies of 400–650 meV, evidencing substantial energy loss upon self-trapping. Kinetic analysis shows that oxides with open d-shells localize charge most readily: polaron formation activation barriers are low in all TMOs (0–10 meV), whereas hopping barriers remain much higher (200–350 meV). This work establishes key spectroscopic and kinetic insights, highlighting the trade-off between charge localization and mobility, as well as the critical role of polaron formation in TMOs photocatalysts.
\n
Small polarons remain a bottleneck in realizing efficient transition metal oxide devices. Routes to engineer small polaron coupling to electronic states and lattice modes to control carrier localization remain unclear. Here, we measure small polaron formation in CuFeO2 using transient extreme ultraviolet reflection spectroscopy and compare to theoretical predictions in realistically parametrized Holstein models, demonstrating that polaron localization depends on coupling to high-frequency versus low-frequency phonon bath components. We measure small polaron formation on a comparable ∼100 fs timescale to other Fe(III) compounds. Dynamic delocalization of the polaron follows formation through a coherent lattice expansion between Fe-O layers and charge-sharing with surrounding Fe(IV) states. Simulations reveal two major factors dictate polaron formation timescales: phonon density and reorganization energy distributions between acoustic and optical modes, matching experimental findings. Our work shows how electronic-structural coupling in a polaron-host material can be leveraged to suppress polaronic effects for various applications.
",
"doi": "10.1021/acs.jpclett.5c03430",
"issn": "1948-7185",
"publisher": "American Chemical Society",
"publication": "Journal of Physical Chemistry Letters",
"publication_date": "2026-01-15",
"series_number": "2",
"volume": "17",
"issue": "2",
"pages": "656-664"
},
{
"id": "authors:dhec0-aaz16",
"collection": "authors",
"collection_id": "dhec0-aaz16",
"cite_using_url": "https://authors.library.caltech.edu/records/dhec0-aaz16",
"type": "article",
"title": "Nanoscale and Element-Specific Lattice Temperature Measurements Using Core-Loss Electron Energy-Loss Spectroscopy",
"author": [
{
"family_name": "Palmer",
"given_name": "Levi D.",
"orcid": "0000-0002-7228-4263",
"clpid": "Palmer-Levi-D"
},
{
"family_name": "Lee",
"given_name": "Wonseok",
"orcid": "0000-0003-1077-0511",
"clpid": "Lee-Wonseok"
},
{
"family_name": "Durham",
"given_name": "Daniel B.",
"orcid": "0000-0002-5780-6852"
},
{
"family_name": "Fajardo",
"given_name": "Javier",
"orcid": "0000-0003-0612-7953"
},
{
"family_name": "Liu",
"given_name": "Yuzi",
"orcid": "0000-0002-8733-1683"
},
{
"family_name": "Talin",
"given_name": "A. Alec",
"orcid": "0000-0002-1102-680X"
},
{
"family_name": "Gage",
"given_name": "Thomas E."
},
{
"family_name": "Cushing",
"given_name": "Scott K.",
"orcid": "0000-0003-3538-2259",
"clpid": "Cushing-S-K"
}
],
"abstract": "\n
Measuring nanoscale local temperatures, particularly in vertically integrated and multicomponent systems, remains challenging. Spectroscopic techniques like X-ray absorption and core-loss electron energy-loss spectroscopy (EELS) are sensitive to lattice temperature, but understanding thermal effects is nontrivial. This work explores the potential for nanoscale and element-specific core-loss thermometry by comparing the Si L2,3 edge’s temperature-dependent redshift against plasmon energy expansion thermometry (PEET) in a scanning TEM. Using density functional theory (DFT), time-dependent DFT, and the Bethe–Salpeter equation, we ab initio model both the Si L2,3 and plasmon redshift. We find that the core-loss redshift occurs due to bandgap reduction from electron–phonon renormalization. Our results indicate that despite lower core-loss signal intensity compared to plasmon features, core-loss thermometry has key advantages and can be more accurate through standard spectral denoising. Specifically, we show that the Varshni equation easily interprets the core-loss redshift for semiconductors, which avoids plasmon spectral convolution for PEET in complex junctions and interfaces. We also find that core-loss thermometry is more accurate than PEET at modeling thermal lattice expansion in semiconductors, unless the specimen’s temperature-dependent dielectric properties are fully characterized. Furthermore, core-loss thermometry has the potential to measure nanoscale heating in multicomponent materials and stacked interfaces with elemental specificity at length scales smaller than the plasmon’s wave function.
\n
Understanding how to control changes in the electronic structure and related dynamical renormalizations by external driving fields is the key for understanding ultrafast spectroscopy and applications in electronics. Here, we focus on the band gap's modulation by external electric fields and uncover the effect of band dispersion on the gap renormalization. We employ the Green's function formalism using the real-time Dyson expansion to account for dynamical correlations induced by photodoping. The many-body formalism captures the dynamics of systems with long-range interactions, carrier mobility, and variable electron and hole effective mass. We also demonstrate that mean-field simulations based on the Hartree-Fock Hamiltonian, which lacks dynamical correlations, yields a qualitatively incorrect picture of band-gap renormalization. We find the trend that increasing effective mass, thus decreasing mobility, leads to as much as a 6% enhancement in band-gap renormalization. Further, the renormalization is strongly dependent on the degree of photodoping. As the screening induced by free electrons and holes effectively reduces any long-range and interband interactions for highly excited systems, we show that there is a specific turnover point with a minimal band gap. We further demonstrate that the optical gap renormalization follows the same trend though its magnitude is altered by the Moss-Burstein effect.
",
"doi": "10.1103/bpqy-f2pk",
"issn": "2469-9950",
"publisher": "American Physical Society",
"publication": "Physical Review B",
"publication_date": "2025-08-15",
"series_number": "7",
"volume": "112",
"issue": "7",
"pages": "075105"
},
{
"id": "authors:16htd-dqr46",
"collection": "authors",
"collection_id": "16htd-dqr46",
"cite_using_url": "https://authors.library.caltech.edu/records/16htd-dqr46",
"type": "article",
"title": "Approaching the Lower Temporal Limit of Laser-Produced Plasma Sources for Table-Top Soft X-ray NEXAFS Measurements",
"author": [
{
"family_name": "Nimlos",
"given_name": "Danika",
"orcid": "0000-0002-5414-0039",
"clpid": "Nimlos-Danika"
},
{
"family_name": "Arellano",
"given_name": "Alejandro",
"clpid": "Arellano-Alejandro"
},
{
"family_name": "Cushing",
"given_name": "Scott Kevin",
"orcid": "0000-0003-3538-2259",
"clpid": "Cushing-S-K"
}
],
"abstract": "The increasing popularity of time-resolved X-ray absorption measurements for understanding dynamics in molecular and material systems has led to many advances in table-top sources for pulsed X-rays. We report on a table-top laser-produced plasma (LPP) source that can perform soft X-ray (SXR), near-edge X-ray absorption fine structure (NEXAFS) measurements using a laser source with 23\u2005ps pulse duration. The spectrometer's key specifications, such as brilliance, resolution, and stability, are characterized against the more commonly used longer-pulse-duration LPP sources. The 23\u2005ps laser produced approximately an order of magnitude weaker SXR flux than the 8\u2005ns laser for a higher power density due to the smaller total energy absorbed by the plasma. The increased repetition rate, as well as the use of a high line-density X-grating, and a self-referencing scheme still allowed for NEXAFS measurements of Si3N4 and TiO2 thin films with 2.5\u2005minute acquisition times, a resolving power of E/ΔE=424, and a signal-to-noise ratio of 100. It was observed that degradation of the gas jet nozzle led to long-term instability of the source, which can be remediated using alternative nozzle designs. This work demonstrates the feasibility of achieving higher temporal resolution in future time-resolved X-ray absorption measurements using table-top LPP sources.
",
"doi": "10.1002/cphc.202400857",
"issn": "1439-4235",
"publisher": "Wiley",
"publication": "ChemPhysChem",
"publication_date": "2025-05-05",
"series_number": "9",
"volume": "26",
"issue": "9",
"pages": "e202400857"
},
{
"id": "authors:2tk1v-84j29",
"collection": "authors",
"collection_id": "2tk1v-84j29",
"cite_using_url": "https://authors.library.caltech.edu/records/2tk1v-84j29",
"type": "article",
"title": "Electronic topological transitions in cadmium under pressure studied via theoretical and experimental x-ray absorption spectroscopy",
"author": [
{
"family_name": "Hinton",
"given_name": "Jasmine K.",
"orcid": "0000-0003-4417-462X"
},
{
"family_name": "Schacher",
"given_name": "Daniel",
"orcid": "0000-0002-4095-6635"
},
{
"family_name": "Lee",
"given_name": "Wonseok",
"orcid": "0000-0003-1077-0511",
"clpid": "Lee-Wonseok"
},
{
"family_name": "Smith",
"given_name": "G. Alexander",
"orcid": "0000-0001-9701-1328"
},
{
"family_name": "Siska",
"given_name": "Emily"
},
{
"family_name": "Park",
"given_name": "Changyong",
"orcid": "0000-0002-3363-5788"
},
{
"family_name": "Ellison",
"given_name": "Paul B.",
"orcid": "0000-0001-8852-9782"
},
{
"family_name": "Cushing",
"given_name": "Scott K.",
"orcid": "0000-0003-3538-2259",
"clpid": "Cushing-S-K"
},
{
"family_name": "Schwartz",
"given_name": "Craig P.",
"orcid": "0000-0002-4149-2684"
},
{
"family_name": "Lawler",
"given_name": "Keith V.",
"orcid": "0000-0003-1087-5815"
},
{
"family_name": "Salamat",
"given_name": "Ashkan",
"orcid": "0000-0001-6556-7532"
}
],
"abstract": "An electronic topological transition (ETT) in cadmium below 1 GPa is investigated in situ with experimental x-ray absorption spectroscopy and projecting calculated core-valence excitons onto the band structure. These projections are a useful application of the Bethe-Salpeter equation approach that considers many-body effects. The method described herein can be used for systems that are otherwise difficult to probe in situ; therefore, it provides a generalizable approach to identifying and understanding ETTs under high pressure. Although pressure-induced ETTs are often probed using indirect structural responses, our own x-ray diffraction and Raman studies suggest a second-order structural transition around 3 GPa but are largely insensitive to or inconclusive for the previously studied ETT in this region.
",
"doi": "10.1103/physrevb.110.205118",
"issn": "2469-9950",
"publisher": "American Physical Society",
"publication": "Physical Review B",
"publication_date": "2024-11-15",
"series_number": "20",
"volume": "110",
"issue": "20",
"pages": "205118"
},
{
"id": "authors:6s5nn-b4p61",
"collection": "authors",
"collection_id": "6s5nn-b4p61",
"cite_using_url": "https://authors.library.caltech.edu/records/6s5nn-b4p61",
"type": "article",
"title": "Subtleties of nanophotonic lithium niobate waveguides for on-chip evanescent wave sensing",
"author": [
{
"family_name": "Harper",
"given_name": "Nathan A.",
"orcid": "0000-0001-8727-0932",
"clpid": "Harper-Nathan-A"
},
{
"family_name": "Hwang",
"given_name": "Emily Y.",
"orcid": "0000-0002-9541-5887",
"clpid": "Hwang-Emily-Y"
},
{
"family_name": "Kocheril",
"given_name": "Philip A.",
"orcid": "0000-0002-1265-5931",
"clpid": "Kocheril-Philip-A"
},
{
"family_name": "Lam",
"given_name": "Tze King"
},
{
"family_name": "Cushing",
"given_name": "Scott Kevin",
"orcid": "0000-0003-3538-2259",
"clpid": "Cushing-S-K"
}
],
"abstract": "Thin-film lithium niobate (TFLN) is promising for optical sensing due to its high nonlinearities, but its material properties present unique design challenges. We compare the sensing performance of the fundamental modes on a TFLN waveguide with a fluorescent dye sample. The TM mode has better overlap with the sample, with a 1.4\u2009\u00d7 greater sample absorption rate versus the TE mode. However, the TM mode also scatters at a 1.4\u2009\u00d7 greater rate, yielding less fluorescence overall. The TE mode is, therefore, more appropriate for sensing. Our findings have important implications for TFLN-based sensor designs.",
"doi": "10.1364/oe.529570",
"issn": "1094-4087",
"publisher": "Optica Publishing Group",
"publication": "Optics Express",
"publication_date": "2024-07-29",
"series_number": "16",
"volume": "32",
"issue": "16",
"pages": "27931"
},
{
"id": "authors:4dsy7-g1d84",
"collection": "authors",
"collection_id": "4dsy7-g1d84",
"cite_using_url": "https://authors.library.caltech.edu/records/4dsy7-g1d84",
"type": "article",
"title": "Ultrafast Formation of Charge Transfer Trions at Molecular\u2010Functionalized 2D MoS\u2082 Interfaces",
"author": [
{
"family_name": "Jing",
"given_name": "Yuancheng",
"orcid": "0009-0002-0962-2466",
"clpid": "Jing-Yuancheng"
},
{
"family_name": "Liang",
"given_name": "Kangkai",
"clpid": "Liang-Kangkai"
},
{
"family_name": "Muir",
"given_name": "Nicole",
"orcid": "0009-0004-7283-1994",
"clpid": "Mour-Nicole-S"
},
{
"family_name": "Zhou",
"given_name": "Hao",
"clpid": "Zhou-Hao"
},
{
"family_name": "Li",
"given_name": "Zhehao",
"clpid": "Li-Zhehao"
},
{
"family_name": "Palasz",
"given_name": "Joseph",
"orcid": "0000-0002-9825-6981",
"clpid": "Palasz-Joseph-M"
},
{
"family_name": "Sorbie",
"given_name": "Jonathan",
"orcid": "0009-0009-7125-1353",
"clpid": "Sorbie-Jonathan"
},
{
"family_name": "Wang",
"given_name": "Chenglai",
"orcid": "0000-0002-0160-4418",
"clpid": "Wang-Chenglai"
},
{
"family_name": "Cushing",
"given_name": "Scott",
"orcid": "0000-0003-3538-2259",
"clpid": "Cushing-S-K"
},
{
"family_name": "Kubiak",
"given_name": "Clifford",
"orcid": "0000-0003-2186-488X",
"clpid": "Kubiak-Clifford"
},
{
"family_name": "Sofer",
"given_name": "Zden\u011bk",
"orcid": "0000-0002-1391-4448",
"clpid": "Sofer-Zden\u011bk"
},
{
"family_name": "Li",
"given_name": "Shaowei",
"clpid": "Li-Shaowei"
},
{
"family_name": "Xiong",
"given_name": "Wei",
"orcid": "0000-0002-7702-0187",
"clpid": "Xiong-Wei"
}
],
"abstract": "\n\n\n
\n
In this work, we investigate trion dynamics occurring at the heterojunction between organometallic molecules and a monolayer transition metal dichalcogenide (TMD) with transient electronic sum frequency generation (tr-ESFG) spectroscopy. By pumping at 2.4 eV with laser pulses, we have observed an ultrafast hole transfer, succeeded by the emergence of charge-transfer trions. This observation is facilitated by the cancellation of ground state bleach and stimulated emission signals due to their opposite phases, making tr-ESFG especially sensitive to the trion formation dynamics. The presence of charge-transfer trion at molecular functionalized TMD monolayers suggests the potential for engineering the local electronic structures and dynamics of specific locations on TMDs and offers the potential for transferring unique electronic attributes of TMD to the molecular layers.
\n
\n\n
",
"doi": "10.1002/anie.202405123",
"issn": "1433-7851",
"publisher": "Wiley",
"publication": "Angewandte Chemie International Edition",
"publication_date": "2024-05-07",
"pages": "e202405123"
},
{
"id": "authors:5cg7f-40468",
"collection": "authors",
"collection_id": "5cg7f-40468",
"cite_using_url": "https://authors.library.caltech.edu/records/5cg7f-40468",
"type": "article",
"title": "Determining Quasi-Equilibrium Electron and Hole Distributions of Plasmonic Photocatalysts Using Photomodulated X-ray Absorption Spectroscopy",
"author": [
{
"family_name": "Palmer",
"given_name": "Levi Daniel",
"orcid": "0000-0002-7228-4263",
"clpid": "Palmer-Levi-Daniel"
},
{
"family_name": "Lee",
"given_name": "Wonseok",
"orcid": "0000-0003-1077-0511",
"clpid": "Lee-Wonseok"
},
{
"family_name": "Dong",
"given_name": "Chung-Li",
"orcid": "0000-0002-4289-4677",
"clpid": "Dong-Chung-Li"
},
{
"family_name": "Liu",
"given_name": "Ru-Shi",
"orcid": "0000-0002-1291-9052",
"clpid": "Liu-Ru-Shi"
},
{
"family_name": "Wu",
"given_name": "Nianqiang",
"orcid": "0000-0002-8888-2444",
"clpid": "Wu-Nianqiang"
},
{
"family_name": "Cushing",
"given_name": "Scott Kevin",
"orcid": "0000-0003-3538-2259",
"clpid": "Cushing-S-K"
}
],
"abstract": "\n
Most photocatalytic and photovoltaic devices operate under broadband, constant illumination. Electron and hole dynamics in these devices, however, are usually measured by using ultrafast pulsed lasers in a narrow wavelength range. In this work, we use excited-state X-ray theory originally developed for transient X-ray experiments to study steady-state photomodulated X-ray spectra. We use this method to attempt to extract electron and hole distributions from spectra collected at a nontime-resolved synchrotron beamline. A set of plasmonic metal core–shell nanoparticles is designed as the control experiment because they can systematically isolate photothermal, hot electron, and thermalized electron–hole pairs in a TiO2 shell. Steady-state changes in the Ti L2,3 edge are measured with and without continuous-wave illumination of the nanoparticle’s localized surface plasmon resonance. The results suggest that within error the quasi-equilibrium carrier distribution can be determined even from relatively noisy data with mixed excited-state phenomena. Just as importantly, the theoretical analysis of noisy data is used to provide guidelines for the beamline development of photomodulated steady-state spectroscopy.
\n
Polarons are prevalent in condensed matter systems with strong electron-phonon coupling. The adiabaticity of the polaron relates to its transport properties and spatial extent. To date, only adiabatic small polaron formation has been measured following photoexcitation. The lattice reorganization energy is large enough that the first electron–optical phonon scattering event creates a small polaron without requiring substantial carrier thermalization. We measure that frustrating the iron-centered octahedra in the rare-earth orthoferrite ErFeO3 leads to antiadiabatic polaron formation. Coherent charge hopping between neighboring Fe3+\u2500Fe2+ sites is measured with transient extreme ultraviolet spectroscopy and lasts several picoseconds before the polaron forms. The resulting small polaron formation time is an order of magnitude longer than previous measurements and indicates a shallow potential well, even in the excited state. The results emphasize the importance of considering dynamic electron-electron correlations, not just electron-phonon–induced lattice changes, for small polarons for transport, catalysis, and photoexcited applications.
\n\n",
"doi": "10.1126/sciadv.adk4282",
"pmcid": "PMC10954221",
"issn": "2375-2548",
"publisher": "American Association for the Advancement of Science",
"publication": "Science Advances",
"publication_date": "2024-03-22",
"series_number": "12",
"volume": "10",
"issue": "12",
"pages": "eadk4282"
},
{
"id": "authors:ddqtb-nxf63",
"collection": "authors",
"collection_id": "ddqtb-nxf63",
"cite_using_url": "https://authors.library.caltech.edu/records/ddqtb-nxf63",
"type": "article",
"title": "Experimental upper bounds for resonance-enhanced entangled two-photon absorption cross section of indocyanine green",
"author": [
{
"family_name": "He",
"given_name": "Manni",
"orcid": "0009-0001-4237-900X",
"clpid": "He-Manni"
},
{
"family_name": "Hickam",
"given_name": "Bryce P.",
"orcid": "0000-0003-2120-4769",
"clpid": "Hickam-Bryce-P"
},
{
"family_name": "Harper",
"given_name": "Nathan",
"orcid": "0000-0001-8727-0932",
"clpid": "Harper-Nathan"
},
{
"family_name": "Cushing",
"given_name": "Scott K.",
"orcid": "0000-0003-3538-2259",
"clpid": "Cushing-S-K"
}
],
"abstract": "\n\n\n
Resonant intermediate states have been proposed to increase the efficiency of entangled two-photon absorption (ETPA). Although resonance-enhanced ETPA (r-ETPA) has been demonstrated in atomic systems using bright squeezed vacuum, it has not been studied in organic molecules. We investigate for the first time r-ETPA in an organic molecular dye, indocyanine green (ICG), when excited by broadband entangled photons in near-IR. Similar to many reported virtual state mediated ETPA (v-ETPA) measurements, no r-ETPA signals are measured, with an experimental upper bound for the cross section placed at 6(±2) × 10−23 cm2. In addition, the classical resonance-enhanced two-photon absorption (r-TPA) cross section of ICG at 800 nm is measured for the first time to be 20(±13) GM, where 1 GM equals 10−50 cm4 s, suggesting that having a resonant intermediate state does not significantly enhance two-photon processes in ICG. The spectrotemporally resolved emission signatures of ICG excited by entangled photons are also presented to support this conclusion.
\n\n