A5066126022- Topological Materials and Phenomena
- Graphene research and applications
- Advanced Condensed Matter Physics
- 2D Materials and Applications
- Physics of Superconductivity and Magnetism
- Rare-earth and actinide compounds
- Terahertz technology and applications
- Photorefractive and Nonlinear Optics
- Phase-change materials and chalcogenides
- Magnetic properties of thin films
- Quantum and electron transport phenomena
- Iron-based superconductors research
- Magnetic and transport properties of perovskites and related materials
- Multiferroics and related materials
- Magneto-Optical Properties and Applications
- Superconducting and THz Device Technology
- Quantum many-body systems
- Quantum, superfluid, helium dynamics
- Electric Motor Design and Analysis
- Photonic and Optical Devices
- Magnetic Properties of Alloys
- Mechanical and Optical Resonators
- Electronic and Structural Properties of Oxides
- Magnetic Bearings and Levitation Dynamics
- Acoustic Wave Resonator Technologies
California University of Pennsylvania
2018-2025
University of Pennsylvania
2017-2024
Guizhou Normal University
2024
Wuhan University
2018-2022
Johns Hopkins University
2012-2020
University of Surrey
2020
Instituto de Ciencias Agrarias
2020
Lawrence Berkeley National Laboratory
2017-2018
University of California, Berkeley
1988-2018
State Key Laboratory of Automotive Simulation and Control
2018
Time-domain terahertz polarimetry is used to measure the fine-structure constant in solid state.
We report the THz response of thin films topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$. At low frequencies, transport is essentially thickness independent showing dominant contribution surface electrons. Despite their extended exposure to ambient conditions, these surfaces exhibit robust properties including narrow, almost thickness-independent Drude peaks, and an unprecedentedly large polarization rotation linearly polarized light reflected in applied magnetic field. This Kerr...
Material defects remain as the main bottleneck to progress of topological insulators (TIs). In particular, efforts achieve thin TI samples with dominant surface transport have always led increased and degraded mobilities, thus making it difficult probe quantum regime states. Here, by utilizing a novel buffer layer scheme composed an In2Se3/(Bi0.5In0.5)2Se3 heterostructure, we introduce generation Bi2Se3 films order magnitude enhanced mobilities than before. This has first observation Hall...
Optical reflectivity experiments on Cd${}_{3}$As${}_{2}$ indicate the presence of Kane electrons rather than Dirac fermions in this material. The results contradict those from recent ARPES experiments, but agree with STM results.
The second-order conductivity of a material, ${\ensuremath{\sigma}}^{(2)}$, relating current to the square electric field, is nonzero only when inversion symmetry broken, unlike conventional linear conductivity. Second-order nonlinear optical responses are thus powerful tools in basic research as probes breaking; they also central technology basis for generating photocurrents and frequency doubling. recent surge interest Weyl semimetals with acentric crystal structures has led discovery host...
We report measurements of optical absorption in the zig-zag antiferromagnet $\alpha$-RuCl$_3$ as a function temperature, $T$, magnetic field, $B$, and photon energy, $\hbar\omega$ range $\sim$ 0.3 to 8.3 meV, using time-domain terahertz spectroscopy. Polarized show that 3-fold rotational symmetry is broken honeycomb plane from 2 K 300 K. find sharp peak at 2.56 meV upon cooling below N\'eel temperature 7 $B=0$ we identify magnetic-dipole excitation zero-wavevector magnon, or...
Based on specific heat and magnetoresistance measurements, we report that a "heavy" electronic state exists below $T \approx$ 20 K in KNi$_2$Se$_2$, with an increased carrier mobility enhanced effective band mass, $m$* = 6$m_b$ to 18$m_b$. This evolves into superconductivity at $T_c$ 0.80(1) K. These properties resemble of many-body heavy-fermion state, which derives from the hybridization between localized magnetic states conduction electrons. Yet, no evidence for magnetism or order is...
We have utilized time-domain magnetoterahertz spectroscopy to investigate the low-frequency optical response of topological insulator ${\mathrm{Cu}}_{0.02}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ and ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ films. With both field frequency dependence, such experiments give sufficient information measure mobility carrier density multiple conduction channels simultaneously. observe sharp cyclotron resonances (CRs) in materials. The small amount Cu incorporated into...
It has been proposed that topological insulators can be best characterized not as surface conductors, but bulk magnetoelectrics -- under the right conditions-- have a universal quantized magnetoelectric response coefficient $e^2/2h$. However, it is clear to what extent these conditions are achievable in real materials disorder, finite chemical potential, residual dissipation, and even inversion symmetry. This led some confusion misconceptions. The primary goal of this work illustrate exactly...
Second-harmonic generation has been applied to study lattice, electronic, and magnetic proprieties in atomically thin materials. However, inversion symmetry breaking is usually required for the materials generate a large signal. In this work, we report giant second-harmonic that arises below Néel temperature few-layer centrosymmetric FePS3. A layer-dependent indicates detected signal from second-order nonlinearity of surface. The magnetism-induced surface response 2 orders magnitude larger...
The Kitaev quantum spin liquid (KSL) is a theoretically predicted state of matter whose fractionalized quasiparticles are distinct from bosonic magnons, the fundamental excitation in ordered magnets. layered honeycomb antiferromagnet $\alpha$-RuCl$_3$ KSL candidate material, as it can be driven to magnetically disordered phase by application an in-plane magnetic field, with $H_c \sim 7$ T. Here we report detailed characterization spectrum this material high-resolution time-domain terahertz...
We report the optical conductivity in high-quality crystals of chiral topological semimetal CoSi, which hosts exotic quasiparticles known as multifold fermions. find that response is separated into several distinct regions a function frequency, each dominated by different types quasiparticles. The low-frequency intraband captured narrow Drude peak from high-mobility electron pocket double Weyl quasi-particles, and temperature dependence spectral weight consistent with its Fermi velocity. By...
We have developed a sensitive cryogenic second-harmonic generation microscopy to study van der Waals antiferromagnet MnPS_{3}. find that long-range Néel antiferromagnetic order develops from the bulk crystal down bilayer, while it is absent in monolayer. Before entering ordered phase all samples, an upturn of second harmonic below 200 K indicates formation short-range and magnetoelastic coupling. also directly image two antiphase (180°) domains thermally induced domain switching bilayer. An...
The absence of mirror symmetry, or chirality, is behind striking natural phenomena found in systems as diverse DNA and crystalline solids. A remarkable example occurs when chiral semimetals with topologically protected band degeneracies are illuminated circularly polarized light. Under the right conditions, part generated photocurrent that switches sign upon reversal light's polarization, known circular photogalvanic effect, predicted to depend only on fundamental constants. conditions...
We report measurement of terahertz anomalous Hall conductivity and Faraday rotation in the magnetic Weyl semimetal ${\mathrm{Co}}_{2}\mathrm{MnGa}$ thin films as a function field, temperature, thickness, using time-domain spectroscopy. The shows thickness-independent around 600 ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ at room it is also frequency-independent from 0.2--1.5 THz. magnitude longitudinal conductivities, weak...
Abstract Kramers nodal lines (KNLs) have recently been proposed theoretically as a special type of Weyl line degeneracy connecting time-reversal invariant momenta. KNLs are robust to spin orbit coupling and inherent all non-centrosymmetric achiral crystal structures, leading unusual spin, magneto-electric, optical properties. However, their existence in real quantum materials has not experimentally established. Here we gather the experimental evidence pointing at presence SmAlSi, metal that...
α -MnTe is an antiferromagnetic semiconductor with above room temperature TN = 310 K, which promising for spintronic applications. Recently, it was reported to be altermagnet, containing bands momentum-dependent spin splitting; time-resolved experimental probes of MnTe are, therefore, important both understanding novel magnetic properties and potential device We investigate ultrafast dynamics in epitaxial MnTe(001)/InP(111) thin films using pump-probe magneto-optical measurements the Kerr...
Superconductivity in disordered systems close to an incipient localization transition has been area of investigation for many years, but fundamentally important aspects are still not understood. It noted that such highly superconductors, anomalous spectral weight develops their conductivity near and below the superconducting gap energy. In this work we investigate low frequency NbN thin films with time-domain terahertz spectroscopy. normal state, strong deviations from Drude form due found....
Abstract Non-volatile phase-change memory devices utilize local heating to toggle between crystalline and amorphous states with distinct electrical properties. Expanding on this kind of switching two topologically phases requires controlled non-volatile symmetries. Here, we report the observation reversible stable closely related crystal structures, remarkably electronic in near-room-temperature van der Waals ferromagnet Fe 5− δ GeTe 2 . We show that is enabled by ordering disordering site...