A5049805033- Topological Materials and Phenomena
- 2D Materials and Applications
- Advanced Condensed Matter Physics
- Graphene research and applications
- Heusler alloys: electronic and magnetic properties
- Magnetic properties of thin films
- Quantum and electron transport phenomena
- Electronic and Structural Properties of Oxides
- Quantum many-body systems
- Rare-earth and actinide compounds
- Perovskite Materials and Applications
- Phase-change materials and chalcogenides
- Magnetic and transport properties of perovskites and related materials
- Photorefractive and Nonlinear Optics
- Physics of Superconductivity and Magnetism
- Iron-based superconductors research
- MXene and MAX Phase Materials
- Crystallization and Solubility Studies
- X-ray Diffraction in Crystallography
- ZnO doping and properties
- Photonic Crystals and Applications
- Advanced Electron Microscopy Techniques and Applications
- Quantum Mechanics and Non-Hermitian Physics
- Inorganic Chemistry and Materials
- Surface and Thin Film Phenomena
Hiroshima University
2015-2025
Japan Atomic Energy Agency
2020-2024
Tokyo Institute of Technology
2019-2022
Kyoto University
2021
Inducing magnetism into topological insulators is intriguing for utilizing exotic phenomena such as the quantum anomalous Hall effect (QAHE) technological applications. While most studies have focused on doping magnetic impurities to open a gap at surface-state Dirac point, many undesirable effects been reported appear in some cases that makes it difficult determine whether opening due time-reversal symmetry breaking or not. Furthermore, realization of QAHE has limited low temperatures. Here...
Recent breakthrough in search for the analogs of fundamental particles condensed matter systems lead to experimental realizations 3D Dirac and Weyl semimetals. state can be hosted either by non-centrosymmetric or magnetic materials first second type. Several have been proposed type-II semimetals, but all them Fermi arcs between projections multiple points not observed directly they were hardly distinguishable from trivial surface states which significantly hinders practical application these...
Abstract Weyl semimetals are characterized by the presence of massless band dispersion in momentum space. When a semimetal meets magnetism, large anomalous transport properties emerge as consequence its topological nature. Here, using in−situ spin- and angle-resolved photoelectron spectroscopy combined with ab initio calculations, we visualize spin-polarized cone flat-band surface states ferromagnetic Co 2 MnGa films full remanent magnetization. We demonstrate that Hall Nernst conductivities...
Abstract We have developed a state-of-the-art apparatus for laser-based spin- and angle-resolved photoemission spectroscopy with micrometer spatial resolution (µ-SARPES). This equipment is realized by the combination of high-resolution photoelectron spectrometer, 6 eV laser high photon flux that focused down to few micrometers, high-precision sample stage control system, double very-low-energy-electron-diffraction spin detector. The setup achieves an energy 1.5 (5.5) meV without (with)...
Abstract Topological insulators (TIs) are a new quantum state of matter. Their surfaces and interfaces act as topological boundary to generate massless Dirac fermions with spin-helical textures. Investigation fermion dynamics near the point (DP) is crucial for future development spintronic devices incorporating insulators. However, research so far has been unsatisfactory because substantial overlap bulk valence band lack completely unoccupied DP. Here, we explore surface in TI Sb 2 Te 3 by...
Abstract Materials that possess nontrivial topology and magnetism is known to exhibit exotic quantum phenomena such as the anomalous Hall effect. Here, we fabricate a novel magnetic topological heterostructure Mn 4 Bi 2 Te 7 /Bi 3 where multiple layers are inserted into topmost quintuple layer of original insulator . A massive Dirac cone (DC) with gap 40–75 meV at 16 K observed. By tracing temperature evolution, this shown gradually decrease increasing blunt transition from massless DC...
Abstract Magnetically doped topological insulators, possessing an energy gap created at the Dirac point through time-reversal-symmetry breaking, are predicted to exhibit exotic phenomena including quantized anomalous Hall effect and a dissipationless transport, which facilitate development of low-power-consumption devices using electron spins. Although several candidates magnetically insulators were demonstrated show long-range magnetic order, realization is so far restricted Cr-doped...
Conventional Rashba spin polarization is caused by the combination of strong spin-orbit interaction and spatial inversion asymmetry. However, Rashba-Dresselhaus-type spin-split states are predicted in centrosymmetric LaOBiS2 system recent theory, which stem from local asymmetry active BiS2 layer. By performing high-resolution spin- angle-resolved photoemission spectroscopy, we have investigated electronic band structure texture superconductor LaO0.55F0.45BiS2. Here present direct...
Abstract A synergistic effect between strong electron correlation and spin–orbit interaction has been theoretically predicted to realize new topological states of quantum matter on Kondo insulators (KIs), so-called (TKIs). One TKI candidate experimentally observed the KI SmB 6 (001), origin surface (SS) order actively discussed. Here, we show a metallic SS clean another YbB 12 (001) using angle-resolved photoelectron spectroscopy. The shows temperature-dependent reconstruction corresponding...
Half-metallic ferromagnets exhibit a perfect spin-polarization at the Fermi energy. Among many candidates, Co2MnSi Heusler alloy is most investigated material due to its half-metallic nature and high Curie temperature (TC). Magnetic junction devices using show remarkable performance low temperatures. However, significantly degraded room temperature, which requires detailed understanding of temperature-dependent electronic structure films. Here, surface-sensitive spin- angle-resolved...
Abstract Topological insulators (TIs) possess spin-polarized Dirac fermions on their surface but unique properties are often masked by residual carriers in the bulk. Recently, (Sb 1− x Bi ) 2 Te 3 was introduced as a non-metallic TI whose carrier type can be tuned from n to p across charge neutrality point. By using time- and angle-resolved photoemission spectroscopy, we investigate ultrafast dynamics series of . The electronic recovery ∼10 ps at most bulk-metallic regime elongated >400...
Chalcogenide phase-change materials show strikingly contrasting optical and electrical properties, which has led to their extensive implementation in various memory devices. By performing spin-, time-, angle-resolved photoemission spectroscopy combined with the first-principles calculation, we report experimental results that crystalline phase of GeSb2Te4 is topologically nontrivial vicinity Dirac semimetal phase. The resulting linearly dispersive bulk Dirac-like bands cross Fermi level are...
The band inversions that generate the topologically non-trivial gaps of topological insulators and isolated Dirac touching points three-dimensional semimetals generally arise from crossings electronic states derived different orbital manifolds. Recently, concept single orbital-manifold occurring along high-symmetry lines has been demonstrated, stabilising multiple bulk surface fermions. Here, we discuss underlying ingredients necessary to achieve such phases, their existence within family...
Fe$_5$GeTe$_2$ is a van der Waals (vdW)-coupled unconventional ferromagnetic metal with high Curie temperature ($T_C$) exceeding 300 K. The formation of an anomalous ground state significantly below $T_C$ has received considerable attention, resulting in increased interest understanding the spin-polarized electronic evolution near Fermi energy ($E_F$) as function temperature. Despite recent extensive studies, microscopic structure around $E_F$ not yet been established owing to intrinsic...
Ferromagnetic topological insulators have emerged as a promising platform for quantum anomalous Hall (QAH) effect with dissipationless edge transport. However, the observation of QAH has so far been restricted to extremely low temperatures. We investigate microscopic origin ferromagnetism coupled in vanadium-doped (${\mathrm{Sb},\mathrm{Bi})}_{2}{\mathrm{Te}}_{3}$ employing x-ray magnetic circular dichroism, angle-resolved two-photon photoemission spectroscopy, combined first-principles...
Transient electron-hole pairs generated in semiconductors can exhibit unconventional excitonic condensation. Anisotropy the carrier mass is considered as key to elongate life time of pairs, and hence stabilize Here we employ time- angle-resolved photoemission spectroscopy explore dynamics photo-generated carriers black phosphorus. The electronic structure above Fermi level has been successfully observed, a massive-and-anisotropic Dirac-type dispersions are confirmed; more importantly,...
The efficient generation of spin-polarized current is one the keys to realizing spintronic devices with a low power consumption. Topological insulators are strong candidates for this purpose. A surface photovoltaic effect can be utilized on topological insulator, where flow upon illumination. Here, we used time- and angle-resolved photoelectron spectroscopy Bi2Te3 demonstrate that magnitude photovoltage almost doubled in optically aged samples, i.e., samples whose has been exposed intense...
Abstract Quantum anomalous Hall effect (QAHE) is a key phenomenon for low power-consumption device applications owing to its dissipationless spin-polarized and quantized current in the absence of an external magnetic field. However, recorded working temperature QAHE still very low. Here we systematically investigate dopants induced modifications from view points magnetic, structural electronic properties ultrafast carrier dynamics series V-doped Sb 2 Te 3 samples composition 2− x V with = 0,...
Controlled extraction of spin-polarized currents from the surface topological insulators (TIs) would be an important step to use TIs as spin-electronic device materials. One way is utilize photovoltage (SPV) effect, by which current may flow upon irradiation light. To date, unipolar SPV has been observed on TIs, while realization ambipolar crucial for taking control over direction flow. By using time-resolved photoemission, we demonstrate realized TI ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. The...
We show Shubnikov-de Haas oscillations in topological insulator (Bi$_{x}$Sb$_{1-x}$)$_{2}$Te$_{3}$ films whose carrier type is p-type (x = 0.29, 0.34) and n-type 0.42). The physical properties such as the Berry phase, mobility, scattering time are significantly changed by tuning Fermi-level position with concentration x. Landau-level fan diagram sample x 0.42 showed $\pi$ phase its mobility was high 17,000 cm$^{2}$/V/s, whereas others had 2$\pi$ much lower mobility. This suggests that...
We successfully fabricated a ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}/{\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ heterostructure by incorporating Mn and Te inside the topmost quintuple layer of ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$, as unambiguously confirmed low-energy electron diffraction $I\text{\ensuremath{-}}V$ scanning transmission microscopy measurements. The surface-state Dirac cone showed little change compared to that pristine x-ray magnetic circular dichroism measurements system was...
We investigated the intrinsic magnetic properties of two-dimensional ferromagnetic candidate monolayer $1T\text{\ensuremath{-}}{\mathrm{VSe}}_{2}$ films using x-ray circular dichroism (XMCD), an element-specific probe. By performing high-resolution measurements, we succeeded in detecting a clear XMCD signal from atomically thin under external field. Through manipulation incidence angle, were able to disentangle in-plane and out-of-plane found strong anisotropy. Moreover, magnetic-field-...
Maintaining a population inversion in electron distributions is the first step towards lasing. There strong interest realizing Dirac conical band structure, because broad-band lasing may then be realized owing to zero-gap nature of cone. Here we show that can elongated $>7$ ps at 8 K and $>10$ 300 on surface $p$-type topological insulator ${({\mathrm{Sb}}_{0.73}{\mathrm{Bi}}_{0.27})}_{2}{\mathrm{Te}}_{3}$. Time- angle-resolved photoemission spectroscopy gives us direct evidence for duration...
Topological insulators (TIs) with an inverted bulk band and a strong spin-orbit coupling exhibit gapless topological surface states (TSSs) protected by time-reversal symmetry. Helical spin textures driven spin-momentum locking offer the opportunity to generate spin-polarized currents therefore TIs are expected be used for future spintronic applications. For practical applications urgently required that operable at room temperature due wide gap as well distinct state is robust atmospheric...