A5042304291- Topological Materials and Phenomena
- Graphene research and applications
- Rare-earth and actinide compounds
- Iron-based superconductors research
- 2D Materials and Applications
- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Quantum and electron transport phenomena
- Magnetic and transport properties of perovskites and related materials
- Advanced Semiconductor Detectors and Materials
- Phase-change materials and chalcogenides
- Advanced Chemical Physics Studies
- Photorefractive and Nonlinear Optics
- Quantum many-body systems
- Catalytic Processes in Materials Science
- High-pressure geophysics and materials
- Terahertz technology and applications
- Advanced Thermoelectric Materials and Devices
- Electronic and Structural Properties of Oxides
- Quantum, superfluid, helium dynamics
- Atmospheric Ozone and Climate
- Atomic and Subatomic Physics Research
- Refrigeration and Air Conditioning Technologies
- Spectroscopy and Laser Applications
- Electric and Hybrid Vehicle Technologies
Kyungpook National University
2022-2023
Max Planck Institute for Chemical Physics of Solids
2018-2021
Los Alamos National Laboratory
2019-2020
Pohang University of Science and Technology
2011-2020
Samsung (South Korea)
2016
North Dakota State University
1991-1998
Mississippi State University
1996
We report the observation of highly anisotropic Dirac fermions in a Bi square net ${\mathrm{SrMnBi}}_{2}$, based on first-principles calculation, angle-resolved photoemission spectroscopy, and quantum oscillations for high-quality single crystals. found that dispersion is generally induced $(\mathrm{SrBi}{)}^{+}$ layer containing double-sized net. In contrast to commonly observed isotropic cone, cone ${\mathrm{SrMnBi}}_{2}$ with large momentum-dependent disparity Fermi velocities...
Using field-angle, temperature, and back-gate-voltage dependence of the weak anti-localization (WAL) universal conductance fluctuations thin Bi1.5Sb0.5Te1.7Se1.3 topological-insulator single crystals, in combination with gate-tuned Hall resistivity measurements, we reliably separated surface conduction topological nature from both bulk topologically trivial conduction. We minimized crystals back-gate tuned Fermi level to bottom-surface band while keeping top insensitive back-gating optimal...
The electronic states of a single Bi(111) bilayer and its edges, suggested as two dimensional topological insulator, are investigated by scanning tunneling spectroscopy (STS) first-principles calculations. Well-ordered films islands with zigzag edges grown epitaxially on cleaved Bi$_{2}$Te$_{2}$Se crystal. calculation shows that the band gap Bi closes formation new but small hybridization due to strong interaction between Bi$_{2}$Te$_{2}$Se. Nevertheless, nature edge state preserved only an...
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTProduct channel dynamics of the cyanato radical + nitric oxide reactionWilliam F. Cooper, Joonbum Park, and John HershbergerCite this: J. Phys. Chem. 1993, 97, 13, 3283–3290Publication Date (Print):April 1, 1993Publication History Published online1 May 2002Published inissue 1 April 1993https://pubs.acs.org/doi/10.1021/j100115a033https://doi.org/10.1021/j100115a033research-articleACS PublicationsRequest reuse permissionsArticle...
We report the valley-selective interlayer conduction of ${\mathrm{SrMnBi}}_{2}$ under in-plane magnetic fields. The $c$-axis resistivity shows clear angular magnetoresistance oscillations indicating coherent conduction. Strong fourfold variation peak in reveals that contribution each Dirac valley is significantly modulated by field orientation. This originates from anisotropic Fermi surfaces with strong disparity momentum-dependent coupling. Furthermore, we found a signature broken symmetry...
Bi2-xSbxTe3-ySey has been argued to exhibit both topological surface states and insulating bulk states, but not yet studied with local probes on the atomic scale. Here we report electronic structures of Bi1.5Sb0.5Te1.7Se1.3 using scanning tunnelling microscopy (STM) spectroscopy (STS). Although there is significant disorder due alloying constituent atoms, cleaved surfaces crystals present a well-ordered hexagonal lattice 10 Å high quintuple layer steps. STS results reflect band structure...
Abstract While two-dimensional (2D) topological insulators (TI’s) initiated the field of materials, only very few materials were discovered to date and direct access their quantum spin Hall edge states has been challenging due material issues. Here, we introduce a new 2D TI material, Sb layer films. Electronic structures ultrathin islands grown on Bi 2 Te Se are investigated by scanning tunneling microscopy. The maps local density clearly identify robust electronic over thickness three...
The microscopic mechanism for Rashba-type band splitting is examined in detail. We show how an asymmetric charge distribution formed when the local orbital angular momentum (OAM) and crystal get interlocked due to surface effects. An electrostatic energy term Hamiltonian appears such OAM- crystal-momentum-dependent placed electric field produced by inversion-symmetry breaking. Analysis using effective shows that, as atomic spin-orbit coupling (SOC) strength increases from weak strong,...
We report a surface-dominant Josephson effect in superconductor-topological insulator-superconductor (S-TI-S) devices, where Bi1.5Sb0.5Te1.7Se1.3 (BSTS) crystal flake was adopted as an intervening TI between Al superconducting electrodes. observed Fraunhofer-type critical current modulation perpendicular magnetic field Al-TI-Al junction for both local and nonlocal biasing. of the differential resistance also neighboring Au-TI-Au normal when it nonlocally biased by junction. In all cases,...
We report the pressure-induced topological quantum phase transition of BiTeI single crystals using Shubnikov-de Haas oscillations bulk Fermi surfaces. The sizes inner and outer FSs Rashba-split bands exhibit opposite pressure dependence up to P = 3.35 GPa, indicating pressure-tunable Rashba effect. Above a critical ~ 2 frequency for surface increases unusually with pressure, shows an abrupt shift. In comparison band structure calculations, we find that these unusual behaviors originate from...
The CN+NO2 reaction was studied using time-resolved infrared diode laser absorption spectroscopy. total rate constant for this over the temperature range 298–650 K fit to expression k1=10−10.30±0.03 exp[(171±32)/T], in reasonable agreement with previous measurements. Branching ratios at room were also measured. dominant product channel is NCO+NO, which accounts 86.8±6.0% of rate. CO2+N2 and CO+N2O channels account 5.6±6.0 7.6±3.2%, respectively. mechanism formation an NCONO intermediate...
Topologically nontrivial surface current is the hallmark of a topological insulator (TI). Its unambiguous identification is, however, plagued by presence trivial channels. Using simultaneous local and nonlocal transport measurements, scientists make high-precision genuine TI-related current.
We investigate the surface and interface states of Bi2Se3 thin films by using second-harmonic generation technique. Distinct from bulk crystals, film show isotropic azimuth dependence intensity, which is attributed to formation randomly oriented domains on in-plane. Based nonlinear susceptibility deduced model fitting, we determine that band bending induced in a space charge region occurs more strongly at facing Al2O3 substrate or capping layer compared with air. demonstrate distinct...
We have demonstrated that the evolution of two-dimensional electron gas (2DEG) system at an interface metal and model topological insulator (TI) Bi$_2$Se$_3$ can be controlled by choosing appropriate kind elements applying a low temperature evaporation procedure. In particular, we found only surface states (TSSs) exist Mn/Bi$_2$Se$_3$ interface, which would useful for implementing electric contact with current channels only. The existence TSSs alone was confirmed angle-resolved photoemission...
Kondo insulators are expected to transform into metals under a sufficiently strong magnetic field. The closure of the insulating gap stems from coupling field electron spin, yet required strength field-typically order 100 T-means that very little is known about this insulator-metal transition. Here we show Ce[Formula: see text]Bi[Formula: text]Pd[Formula: text], owing its fortuitously small gap, provides an ideal insulator for investigation. A metallic Fermi liquid state established above...
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA diode laser study of the isocyanate + nitrogen dioxide reactionJoonbum Park and John F. HershbergerCite this: J. Phys. Chem. 1993, 97, 51, 13647–13652Publication Date (Print):December 1, 1993Publication History Published online1 May 2002Published inissue 1 December 1993https://pubs.acs.org/doi/10.1021/j100153a037https://doi.org/10.1021/j100153a037research-articleACS PublicationsRequest reuse permissionsArticle Views50Altmetric-Citations24LEARN...
We investigated the correlation between electrical transport and mechanical stress in a topological insulator, Bi2Te3, using conductive probe atomic force microscopy an ultrahigh vacuum environment. After directly measuring charge on cleaved Bi2Te3 surface, we found that current density varied with applied load. Current mapping revealed variation of different terraces. The increased low-pressure regime then decreased high-pressure regime. This was explained light combined effect changes...
We present results of measurements resistivity \CAS{} under the combination $c$-axis magnetic field and in-plane uniaxial stress. In unstressed there are two phases. The low-field A phase is a single-component spin-density wave (SDW), with $\mathbf{q} = (\eta, \pm \eta, 1/2)$, high-field B consists microscopically coexisting $(\eta, 1/2)$ -\eta, waves. Pressure along $\langle 100 \rangle$ lattice direction transverse to both these phases, so initially has little effect, however eventually...
We introduce a distinct approach to engineer topologically protected surface state of topological insulator. By covering the insulator, ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{2}\mathrm{Se}$, with Bi monolayer film, original is completely removed and three new spin helical states, originating from emerge different dispersion polarization, through strong electron hybridization. These states play role keeping bulk nature intact. This mechanism provides way create various types channels on top single...
We investigate the surface states of topological insulator (TI) Bi2Se3 thin films grown on Si nanocrystals and Al2O3 substrates by using terahertz (THz) emission spectroscopy. Compared to bulk crystalline Bi2Te2Se, film TIs exhibit distinct behaviors in phase amplitude emitted THz radiation. In particular, shows an anisotropic response with a strong modulation signal its phase. From x-ray diffraction, we find that crystal plane is inclined respect substrate about 0.27°. This structural...