A5002504414- Topological Materials and Phenomena
- Multiferroics and related materials
- Magnetic and transport properties of perovskites and related materials
- Advanced Condensed Matter Physics
- Nanowire Synthesis and Applications
- 2D Materials and Applications
- Semiconductor Quantum Structures and Devices
- Terahertz technology and applications
- Photonic and Optical Devices
- Electronic and Structural Properties of Oxides
- Plasmonic and Surface Plasmon Research
- Transition Metal Oxide Nanomaterials
- GaN-based semiconductor devices and materials
- Quantum and electron transport phenomena
- Advanced Fiber Laser Technologies
- Physics of Superconductivity and Magnetism
- Metamaterials and Metasurfaces Applications
- Laser-Matter Interactions and Applications
- Ferroelectric and Piezoelectric Materials
- Photorefractive and Nonlinear Optics
- High-pressure geophysics and materials
- Graphene research and applications
- Spectroscopy and Laser Applications
- Ga2O3 and related materials
- Perovskite Materials and Applications
Intellectual Ventures (United States)
2022-2025
Bellevue Hospital Center
2022-2024
Center for Integrated Nanotechnologies
2014-2023
Los Alamos National Laboratory
2014-2023
Los Alamos Medical Center
2017-2020
ORCID
2020
Konkuk University
2018
National Yang Ming Chiao Tung University
2018
University at Buffalo, State University of New York
2018
Rutgers, The State University of New Jersey
2012-2015
A key challenge in materials discovery is to find high-temperature superconductors. Hydrogen and hydride have long been considered promising displaying conventional phonon-mediated superconductivity. However, the high pressures required stabilize these restricted their application. Here, we present results from high-throughput computation, considering a wide range of high-symmetry ternary hydrides across periodic table at ambient pressure. This large composition space then reduced by...
Abstract Controlled charge flows are fundamental to many areas of science and technology, serving as carriers energy information, probes material properties dynamics 1 a means revealing 2,3 or even inducing 4,5 broken symmetries. Emerging methods for light-based current control 5–16 offer particularly promising routes beyond the speed adaptability limitations conventional voltage-driven systems. However, optical generation manipulation currents at nanometre spatial scales remains basic...
We use optical-pump terahertz-probe spectroscopy to investigate the near-threshold behavior of photoinduced insulator-to-metal (IM) transition in vanadium dioxide thin films. Upon approaching ${T}_{c}$ a reduction fluence required drive IM is observed, consistent with softening insulating state due an increasing metallic volume fraction (below percolation limit). This phase coexistence facilitates growth homogeneous conducting following superheating via photoexcitation. A simple dynamic...
We experimentally demonstrate efficient third harmonic generation from an indium tin oxide (ITO) nanofilm (lambda/42 thick) on a glass substrate for pump wavelength of 1.4 um. A conversion efficiency 3.3x10^-6 is achieved by exploiting the field enhancement properties epsilon-near-zero (ENZ) mode with factor 200. This nanoscale frequency method applicable to other plasmonic materials and reststrahlen in proximity longitudinal optical phonon frequencies.
We present a systematic study of both the temperature and frequency dependence optical response in TaAs, material that has recently been realized to host Weyl semimetal state. Our reveals conductivity TaAs features narrow Drude alongside conspicuous linear on frequency. The width peak decreases upon cooling, following $T^{2}$ which is expected for semimetals. Two components with distinct slopes dominate 5-K conductivity. A comparison between our experimental results theoretical calculations...
We systematically measured the Hall effect in extremely large magnetoresistance semimetal WTe2. By carefully fitting resistivity to a two-band model, temperature dependencies of carrier density and mobility for both electron- hole-type carriers were determined. observed sudden increase hole below ∼160 K, which is likely associated with temperature-induced Lifshitz transition reported by previous photoemission study. In addition, more pronounced reduction electron occurs 50 giving rise...
Ultrafast photoinduced phase transitions could revolutionize data-storage and telecommunications technologies by modulating signals in integrated nanocircuits at terahertz speeds. In quantum phase-changing materials (PCMs), microscopic charge, lattice, orbital degrees of freedom interact cooperatively to modify macroscopic electrical optical properties. Although these interactions are well documented for bulk single crystals thin films, little is known about the ultrafast dynamics...
Black TiO2 nanoparticles with a crystalline-core and amorphous-shell structure exhibit superior optoelectronic properties in comparison pristine TiO2. The fundamental mechanisms underlying these enhancements, however, remain unclear, largely due to the inherent complexities limitations of powder materials. Here, we fabricate homojunction films consisting an oxygen-deficient amorphous layer on top highly crystalline layer, simulate structural/functional configuration black nanoparticles....
We investigate polarization-dependent ultrafast photocurrents in the Weyl semimetal TaAs using terahertz (THz) emission spectroscopy. Our results reveal that highly directional, transient are generated along noncentrosymmetric $c$ axis regardless of incident light polarization, while helicity-dependent excited within $ab$ plane. This is consistent with earlier static photocurrent experiments, and demonstrates on basis both physical constraints imposed by symmetry temporal dynamics intrinsic...
Relaxor ferroelectrics are important in technological applications due to strong electromechanical response, energy storage capacity, electrocaloric effect, and pyroelectric conversion properties. Current efforts discover design materials this class generally rely on substitutional doping as slight changes local compositional order can significantly affect the Curie temperature, morphotropic phase boundary, responses. In work, we demonstrate that moving limit of complexity an ABO3 perovskite...
In light of breakthroughs in superconductivity under high pressure, and considering that record critical temperatures (T c s) across various systems have been achieved the primary challenge for higher T should no longer solely be to increase extreme conditions but also reduce, or ideally eliminate, need applied pressure retaining pressure-induced -enhanced superconductivity. The topological semiconductor Bi 0.5 Sb 1.5 Te 3 (BST) was chosen demonstrate our approach addressing this exploring...
Abstract Understanding and controlling the antiferromagnetic order in multiferroic materials on an ultrafast time scale is a long standing area of interest, due to their potential applications spintronics magnetoelectric switching. We present optical pump-terahertz (THz) probe study Eu 0.75 Y 0.25 MnO 3 . The pump predominantly excites d-d transitions Mn 3+ ions, temporal evolution pump-induced transient conductivity measured with subsequent THz pulse. Two distinct, temperature-dependent...
We demonstrate a nanoscale, subpicosecond (ps) metamaterial device capable of terabit/second all-optical communication in the near-IR. The 600 fs response, 2 orders magnitude faster than previously reported, is achieved by accessing unused regime high-injection level, carrier dynamics α-Si dielectric layer metamaterial. Further, we utilize unrecognized, higher-order, shorter-wavelength negative-index resonance fishnet structure, thereby extending functionality (via structural tuning...
We report a comprehensive study of ultrafast carrier dynamics in single crystals multiferroic BiFeO$_{3}$. Using femtosecond optical pump-probe spectroscopy, we find that the photoexcited electrons relax to conduction band minimum through electron-phonon coupling with $\sim$1 picosecond time constant does not significantly change across antiferromagnetic transition. Photoexcited subsequently leave and primarily decay via radiative recombination, which is supported by photoluminescence...
Strong coupling between discrete phonon and continuous electron-hole pair excitations can give rise to a pronounced asymmetry in the line shape, known as Fano resonance. This effect has been observed variety of systems, such stripe-phase nickelates, graphene high-$T_{c}$ superconductors. Here, we reveal explicit evidence for strong an infrared-active $A_1$ electronic transitions near Weyl points (Weyl fermions) through observation resonance recently discovered semimetal TaAs. The resultant...
WTe${}_{2}$ has recently been reported to exhibit extremely large magnetoresistance, which may find potential applications in devices such as highly sensitive magnetic sensors and hard drives. In this paper, using ultrafast optical spectroscopy, the authors track relaxation of photoexcited carriers time domain they return equilibrium WTe${}_{2}$. Their experimental results not only resolve scales that ultimately limit material electronic devices, e.g., high-speed drives, but also shed new...
We use optical pump–THz probe spectroscopy at low temperatures to study the hot carrier response in thin Bi2Se3 films of several thicknesses, allowing us separate bulk from surface transient response. find that for thinner photoexcitation changes transport scattering rate and reduces THz conductivity, which relaxes within 10 picoseconds (ps). For thicker films, conductivity increases upon scales with increasing both film thickness fluence, a decay time approximately 5 ps as well much higher...
Abstract Nanoscale metamaterials exhibit extraordinary optical properties and are proposed for various technological applications. Here, a new class of novel nanoscale two‐phase hybrid is achieved by combining two major classes traditional plasmonic materials, metals (e.g., Au) transition metal nitrides TaN, TiN, ZrN) in an epitaxial thin film form via the vertically aligned nanocomposite platform. By properly controlling nucleation phases, artificial lattices (APLs) consisting highly...
The discovery of two-dimensional systems hosting intrinsic magnetic order represents a seminal addition to the rich landscape van der Waals materials. CrI3 is an archetypal example, where interdependence structure and magnetism, along with strong light-matter interactions, provides new platform explore optical control vibrational degrees freedom at nanoscale. However, nature magneto-structural coupling on its ultrafast timescale remains crucial open question. Here, we probe dynamics in bulk...
Abstract Semiconductor nanowires (NWs) are nanostructures with a number of novel optical and electronic properties that offer great promise for applications in areas including nanoelectronics, thermoelectrics, sensing, nanophotonics. To realize the full potential these unique nanosystems, however, deep understanding their response to excitation on sub‐picosecond time scale is required. Here, we review recent ultrafast studies carrier dynamics semiconductor NWs. These experiments have been...
To understand the critical factor(s) that influence short-circuit current in poly(3-hexylthiophene) (P3HT)/ZnO solar cells, we investigate morphology of interfacial polymer layer and photoexcitation dynamics picosecond regime. Thin (∼6 nm) films P3HT deposited on bare ZnO modified with an alkanethiol monolayer are used as model systems for heterojunction interface. Results compared thin glass behavior alone. Synchrotron grazing incidence X-ray diffraction spectra alkanethiol-modified surface...
Recent success in the fabrication of axial and radial core–shell heterostructures, composed one or more layers with different properties, on semiconductor nanowires (NWs) has enabled greater control NW-based device operation for various applications.(1-3) However, further progress toward significant performance enhancements a given application is hindered by limited knowledge carrier dynamics these structures. In particular, strong influence interfaces between NWs transport makes it...
We demonstrate the ultrafast formation of terahertz (THz) metasurfaces through all-optical creation spatially modulated carrier density profiles in a deep-subwavelength GaAs film. The switch-on transient plasmon mode, governed by effective electron mass and electron–phonon interactions, is revealed structured-optical pump THz probe spectroscopy, on time scale 500 fs. By modulating using different fluences, we observe wide tuning electric dipole resonance metasurface from 0.5 to 1.7 THz....