A5023036749- Advanced Condensed Matter Physics
- Iron-based superconductors research
- Rare-earth and actinide compounds
- Electronic and Structural Properties of Oxides
- Magnetic and transport properties of perovskites and related materials
- Physics of Superconductivity and Magnetism
- Magnetic properties of thin films
- Corporate Taxation and Avoidance
- Copper-based nanomaterials and applications
- ZnO doping and properties
- Advanced Thermoelectric Materials and Devices
- 2D Materials and Applications
- Multiferroics and related materials
- Chalcogenide Semiconductor Thin Films
- Transition Metal Oxide Nanomaterials
- Superconductivity in MgB2 and Alloys
- Topological Materials and Phenomena
- High-pressure geophysics and materials
- Intellectual Capital and Performance Analysis
- Nuclear Materials and Properties
- Electron and X-Ray Spectroscopy Techniques
- Organic and Molecular Conductors Research
- Magnetic Properties of Alloys
- Semiconductor materials and devices
- Advanced Chemical Physics Studies
Tokyo University of Science
2013-2024
Waseda University
2022-2024
The University of Tokyo
2008-2018
Kagoshima University
2013
Laser angle-resolved photoemission spectroscopy (ARPES) is employed to investigate the temperature ($T$) dependence of electronic structure in ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ across magnetostructural transition at ${T}_{N}\ensuremath{\sim}140\text{ }\text{ }\mathrm{K}$. A drastic transformation Fermi surface (FS) shape ${T}_{N}$ observed, as expected by first-principles band calculations. Polarization-dependent ARPES and calculations consistently indicate that observed FSs...
Bulk photoemission studies of iron pnictides suggest a role for orbital fluctuations in creating the superconducting state.
Electronic structures of the quantum critical superconductor β-YbAlB4 and its polymorph α-YbAlB4 are investigated by using bulk-sensitive hard x-ray photoemission spectroscopy. From Yb 3d core level spectra, values valence estimated to be ∼2.73 ∼2.75 for α- β-YbAlB4, respectively, thus providing clear evidence fluctuations. The band spectra these compounds also show Yb2+ peaks at Fermi level. These observations establish an unambiguous case a strong mixed criticality first time among heavy...
The detail of electronic structures near the Fermi level in ${\text{URu}}_{2}{\text{Si}}_{2}$ has been investigated employing state-of-art laser angle-resolved photoemission spectroscopy. observation a narrow dispersive band ordered state as well its absence Rh-substituted sample strongly suggest that emergence is clear signature hidden-order transition. temperature dependence band, which appears at onset transition, invokes occurrence periodicity modification state, shown for first time by...
We report the detailed electronic structure of a hole-doped delafossite oxide CuCr${}_{1\ensuremath{-}x}$Mg${}_{x}$O${}_{2}$ ($0\ensuremath{\le}x\ensuremath{\le}0.03$) studied by photoemission spectroscopy (PES), soft x-ray absorption (XAS), and band-structure calculations within local-density approximation $+U$ ($\mathrm{LDA}+U$) scheme. Cr/Cu 3$p$-$3d$ resonant PES reveals that near-Fermi-level leading has primarily Cr $3d$ character with minor contribution from Cu through...
Circular dichroism in the angular distribution of photoelectrons from SrTiO(3):Nb and Cu(x)Bi(2)Se(3) is investigated by 7-eV laser angle-resolved photoemission spectroscopy. In addition to well-known node that occurs circular pattern when incidence plane matches mirror crystal, we show another type crystal vertical electronic state two-dimensional. The flower-shaped patterns occurring around Fermi level Dirac point are explained on equal footings. We out penetration depth topological states...
Recent studies suggest that an exemplary Kondo insulator SmB6 belongs to a new class of topological insulators (TIs), in which non-trivial spin-polarized metallic states emerge on surface upon the formation hybridization gap bulk. Remarkably, bulk resistivity reaches more than 20 Ω cm at 4 K, making candidate for so-called bulk-insulating TI. We here investigate optical-pulse responses by pump-and-probe photoemission spectroscopy. Surface photovoltage effect is observed below ~90 K. This...
We discover the experimental case of a quantum valence criticality leading to breakdown Fermi liquid state.
A detailed low-energy electronic structure of a Kondo insulator ${\mathrm{YbB}}_{12}$ was revealed by synergetic combination ultra-high-resolution laser photoemission spectroscopy (PES) and time-resolved PES. The former confirmed 25-meV pseudogap corresponding to the temperature this material, more importantly, it that 15-meV gap Kondo-peak feature developed below crossover ${T}^{*}\ensuremath{\sim}110\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. In harmony with this, latter discovered very long...
We have performed soft x-ray and ultrahigh-resolution laser-excited photoemission measurements on tetragonal FeSe, which was recently identified as a superconductor. Energy dependent study of valence band is compared to structure calculations yields reasonable assignment partial densities states. However, the sharp peak near Fermi level slightly deviates from calculated energy position, giving rise necessity self-energy correction. also laser experiment FeSe observed suppression intensity...
Low-energy electronic structure of optimally doped ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ is investigated using laser-excited angle-resolved photoemission spectroscopy. The surface state and the CuO chain band that usually overlap ${\text{CuO}}_{2}$ plane derived bands are not detected, thus enabling a clear observation bulk superconducting state. observed bilayer splitting Fermi $\ensuremath{\sim}0.08\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$ along...
We report on the electronic structure of perovskite oxide CaCrO3 using valence-band, core-level, and Cr 2p - 3d resonant photoemission spectroscopy (PES). Despite its antiferromagnetic order, a clear Fermi edge characteristic metal with dominant character is observed in valence band spectrum. The single particle density states are spread over 2 eV, spectral weight distributed two peaks centered at ~ 1.2 eV 0.2 below EF, suggestive coherent incoherent resulting from strong electron-electron...
We report on laser-excited angle-resolved photoemission spectroscopy in the electron-doped cuprate Sm1.85Ce0.15CuO(4-δ). The data show existence of a nodal hole-pocket Fermi surface both normal and superconducting states. prove that its origin is long-range antiferromagnetism by an analysis coherence factors main folded bands. This coexistence antiferrmagnetism superconductivity implies cuprates are two-Fermi-surface superconductors. measured gap hole pocket compatible with d-wave symmetry.
The relationship between the superconducting gap and pseudogap has been subject of controversies. In order to clarify this issue, we have studied $\text{high}\ensuremath{-}{T}_{c}$ superconductor ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ ($x=0.10,14$) by angle-resolved photoemission spectroscopy (ARPES). Through analysis ARPES spectra above below ${T}_{c}$, identified a coherence peak even in antinodal region on top larger energy scale. nearly follows pure...
We have performed a temperature-dependent angle-integrated laser photoemission study of iron oxypnictide superconductors LaFeAsO:F and LaFePO:F exhibiting critical-transition temperatures (${T}_{c}$'s) 26 5 K, respectively. find that high-${T}_{c}$ exhibits pseudogaplike feature extending over $\ensuremath{\sim}0.1\text{ }\text{eV}$ about the Fermi level at 250 whereas such is absent in low-${T}_{c}$ LaFePO:F. also $\ensuremath{\sim}20\text{-meV}$ features signatures superconducting gaps...
By using laboratory x-ray photoemission spectroscopy (XPS) and hard (HX-PES) at a synchrotron facility, we report an empirical semi-quantitative relationship between the valence/core-level spectral weight electrical conductivity in La1−xSrxMnO3 as function of x. In Mn 2p3∕2 HX-PES spectra, observed shoulder structure due to Mn3+ well-screened state. However, intensity x = 0.8 was too small explain its higher than 0.0, which confirms our recent analysis on XPS spectra. The near-Fermi level...
We studied the spectral functions of URu${}_{2}$Si${}_{2}$ in hidden-order state by means ultrahigh-resolution angle-resolved photoemission spectroscopy. High signal-to-noise ratio data uncover existence two anomalous fine structures, namely a ``splitting'' previously reported narrow dispersive band, and small, dispersionless ``satellite'' structure. These structures can be explained neither ordinary bands nor development hybridization states; thus our observation should evoke consideration...
We have studied the electronic structure of ${\mathrm{BaV}}_{10}{\mathrm{O}}_{15}$ across metal-insulator transition with V trimerization by means hard-x-ray photoemission spectroscopy (HAXPES) and mean-field calculations. The $2p$ HAXPES indicates ${\mathrm{V}}^{2.5+}\ensuremath{-}{\mathrm{V}}^{3+}$ charge fluctuation in metallic phase, ${\text{V}}^{2+}\ensuremath{-}{\text{V}}^{3+}$ order insulating phase. is consistent solution where a $3d {a}_{1g}$ electron shared two sites face-sharing...
There are only a handful of materials in nature that exhibit sequential temperature-dependent transitions from paramagnetic metal to ferromagnetic phase and then onto insulator phase. Now, scientists have used spectroscopy theoretical calculations reveal details about such polycrystalline K${}_{2}$Cr${}_{8}$O${}_{1}6$.
In this review, we will discuss the effects of itinerant hole and disorder produced by substitutions on magnetic states polycrystalline delafossite oxide CuCrO 2 having a spin-3/2 antiferromagnetic triangular sublattice. First, show hole-doping substitution nonmagnetic Mg 2+ for Cr 3+ physical properties , origin nontrivial promotion 120° Néel state due to coupling between localized spin. Next, introduced isovalent such as Ag + Cu Al one possibility appearance unusual spin liquid or nematic states.
We have investigated the temporal evolution and fluence dependence of band structure in Ta2Ni0.9Co0.1Se5 by means time- angle-resolved photoemission spectroscopy (tr-ARPES). With 3.00 mJ cm−2 delay time 170 fs, conduction crossing Fermi level (EF) valence reaching EF are observed indicating photoinduced semimetal phase. However, at 70 top does not reach creating a partial gap or pseudogap, transition from excitonic insulator state to is completed. The even with shorter (down 50–70 fs) and/or...
We investigate the doping dependent low-energy, low temperature $(T=5\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ properties of nodal quasiparticles in $d$-wave superconductor ${\mathrm{Bi}}_{2.1}{\mathrm{Sr}}_{1.9}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ (Bi2212). By utilizing ultrahigh resolution laser-excited angle-resolved photoemission spectroscopy, we obtain precise band dispersions near ${E}_{F}$, mean free paths, and scattering rates $(\ensuremath{\Gamma})$...
We have studied the electronic structure of ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{V}}_{13}{\mathrm{O}}_{18}$ $(x=0,0.2,1)$ at different temperatures across trimerization and charge-order transitions using hard x-ray photoemission spectroscopy (HAXPES). The V $2p$ HAXPES indicates ${\mathrm{V}}^{2+}/{\mathrm{V}}^{3+}$ charge order fluctuation in high-temperature tetramer phase, low-temperature trimer intermediate-temperature phase series $x=0,0.2,1$. In valence-band...