A5074932828- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Physics of Superconductivity and Magnetism
- Electronic and Structural Properties of Oxides
- Topological Materials and Phenomena
- Multiferroics and related materials
- Quantum and electron transport phenomena
- Magnetic properties of thin films
- Tribology and Lubrication Engineering
- Graphene research and applications
- Rare-earth and actinide compounds
- Nuclear materials and radiation effects
- Tribology and Wear Analysis
- Machine Learning in Materials Science
- Gear and Bearing Dynamics Analysis
- Atomic and Subatomic Physics Research
- Adsorption and biosorption for pollutant removal
- Semiconductor materials and devices
- Cold Atom Physics and Bose-Einstein Condensates
- Nanomaterials and Printing Technologies
- Adhesion, Friction, and Surface Interactions
- Library Science and Administration
- Surface and Thin Film Phenomena
- Quantum many-body systems
- Advanced Chemical Physics Studies
Institute for Basic Science
2016-2024
Seoul National University
2013-2024
Korea Institute for Advanced Study
2024
Korea Institute of Science and Technology
2006-2020
Cornell University
2015-2017
Sogang University
2006
Seoul National University Hospital
2003
Indiana State University
1979
We propose that existence of local orbital angular momentum (OAM) on the surfaces high-Z materials play a crucial role in formation Rashba-type surface band splitting. Local OAM state Bloch produces asymmetric charge distribution (electric dipole). Presence electric field aligns dipole and results chiral states relevant Rashba- type Therefore, splitting originates from interaction, not Zeeman as proposed original Rashba picture. The characteristic spin structure is formed through spin-orbit...
We report on a fundamental thickness limit of the itinerant ferromagnetic oxide SrRuO(3) that might arise from orbital-selective quantum confinement effects. Experimentally, films remain metallic even for 2 unit cells (uc), but Curie temperature T(C) starts to decrease at 4 uc and becomes zero uc. Using Stoner model, we attributed in density states (N(o)). Namely, thin film geometry, hybridized Ru d(yz,zx) orbitals are terminated by top bottom interfaces, resulting reduction N(o).
We show, by way of tight-binding and first-principles calculations, that a one-to-one correspondence between an electron's crystal momentum $\mathbf{k}$ nonzero orbital angular (OAM) is generic feature surface bands. The OAM forms chiral structure in space much as its spin counterpart Rashba model does, consequence the inherent inversion symmetry breaking at but not spin-orbit interaction. This conventional effect may be called ``orbital effect.'' circular dichroism (CD) angle-resolved...
Theory of Rashba spin-orbit coupling in magnetic metals is worked out from microscopic Hamiltonian describing d-orbitals. When structural inversion symmetry broken, electron hopping between $d$-orbitals generates chiral ordering orbital angular momentum, which combines with atomic to result the interaction. parameter characterizing interaction band-specific, even reversing its sign band band. Large enhancement found recent experiments attributed mixing 3d atoms non-magnetic heavy elements as...
We predict a quantum phase transition from normal to topological insulators in the 5$d$ metal oxide Na$_2$IrO$_3$, where can be driven by change of long-range hopping and trigonal crystal field terms. From first-principles-derived tight-binding Hamiltonian we determine boundary through parity analysis. In addition, our first-principles calculations for Na$_2$IrO$_3$ model structures show that interlayer distance an important parameter existence three-dimensional strong insulator phase. is...
We performed angle resolved photoemission (ARPES) studies on Cu(111) and Au(111) surface states with circularly polarized light. Existence of local orbital angular momentum (OAM) is confirmed as has been predicted to be broadly present in a system an inversion symmetry breaking (ISB). The single band found have chiral OAM spite very small spin-orbit coupling (SOC) Cu, which consistent theoretical prediction. As for Au(111), we observe split bands the inner outer are parallel, unlike Bi2Se3...
Using first-principles calculations, we show that topological quantum phase transitions are driven by external electric fields in thin films of Sb(2)Te(3). The film, as the applied field normal to its surface increases, is transformed from a insulator or vice versa depending on film thickness. We identify band topology directly calculating Z(2) invariant electronic wave functions. dispersion edge states also found be consistent with bulk view bulk-boundary correspondence. present possible...
Recently, α-RuCl3 has attracted much attention as a possible material to realize the honeycomb Kitaev model of quantum-spin-liquid state. Although magnetic properties have been extensively studied, its electronic structure, which is strongly related physics, poorly understood. Here, structure was investigated by photoemission (PE) and inverse-photoemission (IPE) spectroscopies. The band gap directly measured from PE IPE spectra found be 1.9 eV, larger than previously estimated values. Local...
Abstract Spin-phonon coupling (SPC) plays a critical role in numerous intriguing phenomena of transition metal oxides (TMOs). In 3d and 4 d TMOs, the between spin lattice degrees freedom is known to originate from exchange interaction. On other hand, origin SPC 5 TMOs remains be elucidated. To address this issue, we measured phonon spectra pyrochlore iridate Y 2 Ir O 7 using optical spectroscopy. Three infrared-active phonons soften below Néel temperature T N ≈ 170 K, indicating existence...
Correlated electrons in transition metal oxides exhibit a variety of emergent phases. When are confined to single-atomic-layer thickness, experiments so far have shown that they usually lose diverse properties and become insulators. In an attempt extend the range electronic phases oxide, we search for metallic phase monolayer-thick epitaxial SrRuO3 film. Combining atomic-scale epitaxy angle-resolved photoemission measurements, show monolayer is strongly correlated metal. Systematic...
The oxide interfaces between materials with different structural symmetries have been actively studied due to their novel physical properties. However, the investigation of intriguing interfacial phenomena caused by oxygen octahedral tilt (OOT) proximity effect has not fully exploited, as there is still no clear understanding what determines length and underlying control mechanism is. Here, we achieved scalability OOT in SrRuO3 (SRO) epitaxial strain near SRO/SrTiO3 heterointerface. We...
The Rashba effect is one of the most striking manifestations spin-orbit coupling in solids and provides a cornerstone for burgeoning field semiconductor spintronics. It typically assumed to manifest as momentum-dependent splitting single initially spin-degenerate band into two branches with opposite spin polarization. Combining polarization-dependent resonant angle-resolved photoemission measurements density functional theory calculations, we show that "spin-split" model giant system BiTeI...
Abstract 5 d pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full understanding magnetism remains elusive as the associated excitations have proven difficult to access conventional techniques. Here we report Raman spectroscopy study spin dynamics in state Cd 2 Os O 7 . Through comparison between two-magnon scattering and spin-wave theory, confirm large single ion...
Defect engineering is one of the key technologies in materials science, enriching modern semiconductor industry and providing good test-beds for solid-state physics. While homogenous doping prevails conventional defect engineering, various artificial distributions have been predicted to induce desired physical properties host materials, especially associated with symmetry breakings. Here, we show layer-by-layer defect-gradients two-dimensional PtSe2 films developed by selective plasma...
The temperature (T) dependence of the optical conductivity spectra σ(ω) a single crystal SrRuO(3) thin film is studied over T range from 5 to 450 K. We observed significant spectral weights charge transfer and interband d-d transitions across ferromagnetic Curie (T(c) ∼ 150 K). Such was attributed increase in Ru spin moment, which consistent with results density functional theory calculations. scans σ(Ω,T) at fixed frequencies Ω reveal clear T(2) below T(c), demonstrating that Stoner...
We present an effective tight-binding Hamiltonian for Li${}_{2}$IrO${}_{3}$ based on maximally localized Wannier functions states near the Fermi level as obtained from first-principles electronic structure calculations. The majority of orbitals are positioned center site with dominant ${j}_{\mathrm{eff}}=1/2$ character, while relatively small ${j}_{\mathrm{eff}}=3/2$ tails lie three nearest-neighbor sites. Interestingly, spin quantization axis components deviates local octahedral and points...
We present results indicating that Chern insulator states can be achieved in the recently synthesized pristine chromium triiodide (${\mathrm{CrI}}_{3}$) by either electron or hole doping. Our first-principles density-functional-theory calculations confirmed monolayer ${\mathrm{CrI}}_{3}$ show nontrivial number $C$ both valence and conduction bands. By introducing on-site Coulomb interaction epitaxial strain, doped exhibit a series of topological quantum phase transitions between multiple...
We have investigated the electronic structure of double perovskites, Ba2FeReO6 (metallic) and Ca2FeReO6 (insulating) using optical x-ray absorption spectroscopy. By comparing experimental results with density functional theory calculations, we found that could be determined from interaction electron correlation spin–orbit coupling. On other hand, for Ca2FeReO6, lattice distortion are important in determining structure. Additionally, insulating gap is realized by Our work shows subtle...
Abstract Based on first-principles density-functional theory (DFT) calculations, we report that the transition-metal bis-dithiolene, M 3 C 12 S ( = Mn and Fe), complexes can be a two-dimensional (2D) ferromagnetic insulator with nontrivial Chern number. Among various synthetic pathways leading to metal bis-dithiolenes, simplest choice of ligand, Benzene-hexathiol, connecting cations form Kagome lattice is studied following experimental time-reversal symmetric isostructural compound Ni . We...
We investigated the electronic structure of $[{(\mathrm{SrIr}{\mathrm{O}}_{3})}_{m},(\mathrm{SrTi}{\mathrm{O}}_{3})](m=\phantom{\rule{0.16em}{0ex}}1,\phantom{\rule{0.16em}{0ex}}2,\mathrm{and}\phantom{\rule{0.16em}{0ex}}\ensuremath{\infty})$ superlattice (SL) thin films with optical spectroscopy and first principles calculations. Our results confirmed existence ${J}_{\mathrm{eff}}=1/2$ states in SL samples, similar to bulk Ruddlesden-Popper series...