A5021998345- Electronic and Structural Properties of Oxides
- Magnetic and transport properties of perovskites and related materials
- Advanced Condensed Matter Physics
- Rare-earth and actinide compounds
- Semiconductor materials and devices
- Iron-based superconductors research
- Transition Metal Oxide Nanomaterials
- ZnO doping and properties
- Physics of Superconductivity and Magnetism
- Topological Materials and Phenomena
- Integrated Circuits and Semiconductor Failure Analysis
- Gas Sensing Nanomaterials and Sensors
- Ga2O3 and related materials
- Multiferroics and related materials
- Graphene research and applications
- 2D Materials and Applications
- Advanced Chemical Physics Studies
- Inorganic Chemistry and Materials
- Advanced Memory and Neural Computing
- Advancements in Solid Oxide Fuel Cells
- Ferroelectric and Piezoelectric Materials
- Semiconductor materials and interfaces
- Chalcogenide Semiconductor Thin Films
- Nuclear Materials and Properties
- Advanced Materials Characterization Techniques
Tohoku University
2016-2025
High Energy Accelerator Research Organization
2016-2025
Tokyo Institute of Technology
2015-2024
Advanced Institute of Materials Science
2021-2024
Institute of Materials Structure Science
2012-2023
Science Factory
2023
Japan Science and Technology Agency
2007-2022
Spintronics Research Network of Japan
2022
National Institutes for Quantum Science and Technology
2022
The University of Tokyo
2007-2021
Honeycomb structures of group IV elements can host massless Dirac fermions with non-trivial Berry phases. Their potential for electronic applications has attracted great interest and spurred a broad search new materials especially in monolayer structures. We present detailed investigation the \beta 12 boron sheet, which is borophene structure that form spontaneously on Ag(111) surface. Our tight-binding analysis revealed lattice 12-sheet could be decomposed into two triangular sublattices...
Highly reliable TaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ReRAM has been successfully demonstrated. The memory cell shows stable pulse switching with endurance over 10 <sup xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> cycles, sufficient retention exceeding years at 85degC. exhibits high and low resistance states based on the redox reaction mechanism, confirmed by HX-PES directly for first time. An 8 kbit 1T1R array a good...
Topological semimetals materialize a new state of quantum matter where massless fermions protected by specific crystal symmetry host exotic phenomena. Distinct from well-known Dirac and Weyl fermions, structurally-chiral topological are predicted to types characterized large charge, whereas such yet be experimentally established. Here, using angle-resolved photoemission spectroscopy, we demonstrate that transition-metal silicide CoSi hosts two chiral spin-1 fermion double fermion, in the...
We report naturally occurring van der Waals heterostructural single crystals with intrinsic magnetic topological properties.
We study superconducting FeSe $({T}_{\mathrm{c}}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}9\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ exhibiting the tetragonal-orthorhombic structural transition $({T}_{\mathrm{s}}\phantom{\rule{0.16em}{0ex}}\ensuremath{\sim}\phantom{\rule{0.16em}{0ex}}90\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ without any antiferromagnetic ordering, by utilizing angle-resolved photoemission spectroscopy. In detwinned orthorhombic state, energy position of...
We have investigated the changes occurring in electronic structure of digitally controlled SrVO(3) ultrathin films across metal-insulator transition (MIT) by film thickness using situ photoemission spectroscopy. With decreasing thickness, a pseudogap is formed at E(F) through spectral weight transfer from coherent part to incoherent part. The finally evolves into an energy gap that indicative MIT film. observed behavior reproduced layer dynamical-mean-field-theory calculations, and it...
Strong spin-orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong electron-electron interactions is just beginning to be understood. Central this emerging area are 5d transition metal iridium oxides. Here, in pyrochlore iridate Pr2Ir2O7, we identify a non-trivial state with single-point Fermi node protected by cubic time-reversal symmetries, using angle-resolved photoemission spectroscopy first-principles...
We investigate the two-dimensional (2D) highly spin-polarized electron accumulation layers commonly appearing near surface of n-type polar semiconductors BiTeX (X = I, Br, and Cl) by angular-resolved photoemission spectroscopy. Due to polarity strong spin-orbit interaction built in bulk atomic configurations, quantized conduction-band subbands show giant Rashba-type spin-splitting. The characteristic 2D confinement effect is clearly observed also valence-bands down binding energy 4 eV....
We have studied the electronic structure at heterointerface between band insulators ${\mathrm{LaAlO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$ using in situ photoemission spectroscopy. Our experimental results clearly reveal formation of a notched on side due to bending metallic ${\mathrm{LaAlO}}_{3}/{\mathrm{TiO}}_{2}\mathrm{\text{\ensuremath{-}}}{\mathrm{SrTiO}}_{3}$ interface. The structure, however, is absent insulating...
We have investigated electronic band structure of a transparent conducting oxide, Nb-doped anatase TiO2 (TNO), by means first-principles calculations and photoemission measurements. The revealed that Nb 4d orbitals are strongly hybridized with Ti 3d ones to form d-nature conduction band, without impurity states in the in-gap region, resulting high carrier density exceeding 1021 cm-3 excellent optical transparency visible region. Furthermore, we confirmed results valence core-level...
The quantum confinement of strongly correlated electrons in artificial structures provides a platform for studying the behavior Fermi-liquid states reduced dimensions. We report creation and control two-dimensional electron-liquid ultrathin films SrVO(3) grown on Nb:SrTiO(3) substrates, which are oxide that can be varied thickness by single monolayers. Angle-resolved photoemission from SrVO(3)/Nb:SrTiO(3) samples shows metallic well adequately described well-known phase-shift quantization...
The chiral crystal is characterized by a lack of mirror symmetry and inversion center, resulting in the inequivalent right- left-handed structures. In noncentrosymmetric structure, spin momentum electrons are expected to be locked reciprocal space with help spin-orbit interaction. To reveal textures crystals, we investigate electronic structure p-type semiconductor, elemental tellurium, simplest using spin- angle-resolved photoemission spectroscopy. Our data demonstrate that highest valence...
One of key challenges in current material research is to search for new topological materials with inverted bulk-band structure. In insulators, the band inversion caused by strong spin-orbit coupling leads opening a gap entire Brillouin zone, whereas an additional crystal symmetry such as point-group and nonsymmorphic symmetries sometimes prohibits at/on specific points or line momentum space, giving rise semimetals. Despite many theoretical predictions insulators/semimetals associated...
Angle-resolved photoemission spectroscopy using a micro-focused beam spot [micro-angle-resolved (ARPES)] is becoming powerful tool to elucidate key electronic states of exotic quantum materials. We have developed versatile micro-ARPES system based on the synchrotron radiation focused with Kirkpatrick-Baez mirror optics. The mirrors are monolithically installed stage, which driven five-axis motion, and vibrationally separated from ARPES measurement system. Spatial mapping Au photolithography...
Using hard x-ray (HX; hnu=5.95 keV) synchrotron photoemission spectroscopy (PES), we study the intrinsic electronic structure of La(1-x)Sr(x)MnO(3) (LSMO) thin films. Comparison Mn 2p core-levels with soft (SX; hnu approximately 1000 eV) PES shows a clear additional well-screened feature only in HX PES. Takeoff-angle dependent data indicate its bulk (> or =20 A) character. The doping and temperature dependence track ferromagnetism metallicity LSMO series. Cluster model calculations including...
In situ thickness-dependent photoemission spectroscopy (PES) has been performed on SrRuO3 (SRO) layers deposited SrTiO3 substrates to study the structure-induced evolution of electronic structure. The PES spectra showing existence two critical film thicknesses reveal that a metal-insulator transition occurs at thickness 4–5 monolayers (ML) and Ru 4d-derived states around Fermi level (EF) saturates about 15 ML. observed spectral behavior well matches electric magnetic properties surface...
We have examined the thermal stability of TiO2-terminated SrTiO3(100) surfaces obtained by buffered HF etching and widely used as substrates for oxide film growth. In situ coaxial impact-collision ion scattering spectroscopy was to measure composition terminating atomic layer at temperatures up 1000°C, simulating a broad range thin-film growth conditions. The TiO2 termination nonannealed but HF-etched surface found start collapsing low 300°C regardless atmosphere, showing instability...
We have studied the electronic structure of epitaxially grown thin films La$_{1-x}$Sr$_x$FeO$_3$ by {\it in-situ} photoemission spectroscopy (PES) and x-ray absorption (XAS) measurements. The Fe 2$p$ valence-band PES spectra O $1s$ XAS LaFeO$_3$ been successfully reproduced configuration-interaction cluster-model calculation and, except for satellite structure, band-structure calculation.From shift binding energies core levels, chemical potential was found to be shifted downward as $x$...
Well-defined metal-insulator-metal trilayered structures composed of epitaxial Pr0.7Ca0.3MnO3 insulator layers, LaNiO3 bottom electrodes, and Al metal top electrodes were fabricated on LaAlO3 (100) substrates. The I-V characteristics the trilayer show electric-field-induced resistance switching. switching ratio heterostructures was up to 100 when positive negative pulsed voltages applied. Detailed analysis indicates importance both trap-controlled space-charge-limited current Poole–Frenkel...
The spatial distribution of chemical states in resistance-switching devices with a planar-type Pt/CuO/Pt structure has been studied by photoemission electron microscopy. It found that the change resistance occurs application first voltage is caused formation reduction path through CuO channel between Pt electrodes. A detailed analysis suggests Joule-heat-assisted induced current flowing device may play an important role conductive path.
The nature of the pseudogap (PG) in high transition temperature (high Tc) superconducting cuprates has been a major issue condensed matter physics. It is still unclear whether Tc superconductivity can be universally associated with PG formation. Here we provide direct evidence existence phase via angle-resolved photoemission spectroscopy another family superconductor, iron pnictides. Our results reveal composition-dependent formation multiband electronic structure BaFe2(As1−xPx)2. develops...
In the hole-doped cuprates, a small amount of carriers suppresses antiferromagnetism and induces superconductivity. electron-doped on other hand, superconductivity appears only in narrow range high electron concentration ($\sim$ doped Ce content) after reduction annealing, strong antiferromagnetic (AFM) correlation persists superconducting phase. Recently, Pr$_{1.3-x}$La$_{0.7}$Ce$_{x}$CuO$_{4}$ (PLCCO) bulk single crystals annealed by "protect annealing" method showed $T_c$ $\sim$ 27 K for...
Abstract Production of chemical fuels by direct solar energy conversion in a photoelectrochemical cell is great practical interest for developing sustainable system. Various nanoscale designs such as nanowires, nanotubes, heterostructures and nanocomposites have been explored to increase the efficiency water splitting. Here we demonstrate self-organized nanocomposite material concept enhancing photocarrier separation electrochemical conversion. Mechanically robust photoelectrodes are formed...
We present an angle-resolved photoemission study of the electronic structure three-dimensional pyrochlore iridate Nd2Ir2O7 through its magnetic metal-insulator transition. Our data reveal that metallic has a quadratic band, touching Fermi level at Gamma point, similarly to Pr2Ir2O7. The node state is, therefore, common feature phase iridates. Upon cooling below transition temperature, this compound exhibits gap opening with energy shift quasiparticle peaks like band insulator. are strongly...