A5024568998- Physics of Superconductivity and Magnetism
- High-pressure geophysics and materials
- Superconductivity in MgB2 and Alloys
- Machine Learning in Materials Science
- X-ray Diffraction in Crystallography
- Advanced Chemical Physics Studies
- Iron-based superconductors research
- 2D Materials and Applications
- Inorganic Fluorides and Related Compounds
- Quantum, superfluid, helium dynamics
- Electronic and Structural Properties of Oxides
- Magnetic and transport properties of perovskites and related materials
- Crystallization and Solubility Studies
- Rare-earth and actinide compounds
- Inorganic Chemistry and Materials
- Crystallography and molecular interactions
- Topological Materials and Phenomena
- Advanced Condensed Matter Physics
- Perovskite Materials and Applications
- Hydrogen Storage and Materials
- Catalysis and Oxidation Reactions
- Quantum and electron transport phenomena
- Thermal Expansion and Ionic Conductivity
- Spectroscopy and Quantum Chemical Studies
- Electron and X-Ray Spectroscopy Techniques
National Institutes for Quantum Science and Technology
2023-2025
Osaka University
2025
The University of Tokyo
2015-2024
Bunkyo University
2023
RIKEN Center for Emergent Matter Science
2015
Tohoku University
2015
Sendai University
2015
Advanced Institute of Materials Science
2015
A dome-shaped superconducting region appears in the phase diagrams of many unconventional superconductors. In doped band insulators, however, reaching optimal superconductivity by fine-tuning carriers has seldom been seen. We report observation a dome temperature-carrier density diagram MoS(2), an archetypal insulator. By quasi-continuous electrostatic carrier doping achieved through combination liquid and solid gating, we revealed large enhancement transition temperature T(c) occurring at...
Pressure-stabilized hydrides are a new rapidly growing class of high-temperature superconductors which is believed to be described within the conventional phonon-mediated mechanism coupling. Here we report synthesis yttrium hexahydride Im3m-YH$_6$ that demonstrates superconducting transition with T$_c$ = 224 K at 166 GPa, much lower than theoretically predicted (>270 K). The measured upper critical magnetic field B$_c$$_2$(0) YH$_6$ was found 116-158 T, 2-2.5 times larger calculated value. A...
Abstract Kohn–Sham density functional theory (DFT) is the basis of modern computational approaches to electronic structures. Their accuracy heavily relies on exchange-correlation energy functional, which encapsulates electron–electron interaction beyond classical model. As its universal form remains undiscovered, approximated functionals constructed with heuristic are used for practical studies. However, there problems in their and transferability, while any systematic approach improve them...
Abstract In recent years, we have been witnessing a paradigm shift in computational materials science. fact, traditional methods, mostly developed the second half of XXth century, are being complemented, extended, and sometimes even completely replaced by faster, simpler, often more accurate approaches. The new approaches, that collectively label machine learning, their origins fields informatics artificial intelligence, but making rapid inroads all other branches With this mind, Roadmap...
We calculate superconducting transition temperatures ($T_{\rm c}$) in sulfur hydrides H$_{2}$S and H$_{3}$S from first principles using the density functional theory for superconductors. At pressures of $\lesssim$150 GPa, high values $T_{\rm c}$ ($\gtrsim$130 K) observed recent experiment [A. P. Drozdov, M. I. Eremets, A. Troyan, arXiv:1412.0460] are accurately reproduced by assuming that decomposes into $R3m$-H$_{3}$S S. For higher pressures, calculated c}$s $Im3m$-H$_{3}$S systematically...
One of the interesting open questions for high-transition-temperature $({T}_{\mathrm{c}})$ superconductivity in sulfur hydrides is why high-pressure phases ${\mathrm{H}}_{3}\mathrm{S}$ have extremely high ${T}_{\mathrm{c}}$'s. Recently, it has been pointed out that presence Van Hove singularities (VHS) around Fermi level crucial. However, while there quantitative estimates ${T}_{\mathrm{c}}$ based on Migdal-Eliashberg theory, energy dependence density states (DOS) neglected to simplify...
The microscopic origin of the large negative thermal expansion cubic scandium trifluorides (${\mathrm{ScF}}_{3}$) is investigated by performing a set anharmonic free-energy calculations based on density functional theory. We demonstrate that conventional quasiharmonic approximation (QHA) completely breaks down for ${\mathrm{ScF}}_{3}$ and quartic anharmonicity, treated nonperturbatively self-consistent phonon theory, essential to reproduce observed transition from positive expansivity...
We explore high-pressure phase stability and superconductivity of lanthanum hydrides $LaH_m$ (m=4-11,16). predict a hitherto unreported polyhydride $P6/mmm$-$LaH_{16}$ at pressures above 150 GPa; 200 GPa its predicted superconducting $T_C$ is 156 K, critical field $\mu_0$$H_C$(0) ~ 35 T gap up to meV. revisit the recently discovered $LaH_{10}$ find be 259 K (170 GPa) from solving Eliashberg equation 271 in SCDFT which also allowed us compute Coulomb pseudopotential $\mu^*$ for $LaH_{16}$....
We incorporate in the Kohn-Sham self-consistent equation a trained neural-network projection from charge density distribution to Hartree-exchange-correlation potential n → VHxc for possible numerical approach exact scheme. The through newly developed scheme enables us evaluate total energy without explicitly treating formula of exchange-correlation energy. With case study simple model, we show that well-trained achieves accuracy and out model parameter range used training, indicating...
We extend the density-functional theory for superconductors (SCDFT) to take account of dynamical structure screened Coulomb interaction. construct an exchange-correlation kernel in SCDFT gap equation on basis random-phase approximation, where electronic collective excitations such as plasmons are properly treated. Through application fcc lithium under high pressures, we demonstrate that our new gives higher transition temperatures (${T}_{c}$) when plasmon and phonon cooperatively mediate...
Aromatic hydrocarbon macrocycles for phosphorescent organic light-emitting devices with a single-layer architecture were designed.
We theoretically give an infinite number of metastable crystal structures for the superconducting sulfur hydride H$_{x}$S under pressure. It has been thought that predicted H$_{2}$S and H$_{3}$S exhibit low high $T_{\rm c}$ in experiment, respectively. The newly found are long-period modulated crystals where slab-like regions intergrow a microscopic scale. extremely small formation enthalpy H$_{2}$S--H$_{3}$S boundary indicated with first-principles calculations suggests possible alloying...
Density functional theory is the standard for computing electronic structure of materials, which based on a that maps electron density to energy. However, rigorous form not known and has been heuristically constructed by interpolating asymptotic constraints extreme situations, such as isolated atoms uniform gas. Recent studies have demonstrated can be effectively approximated using machine learning (ML) approaches. most ML models do satisfy constraints. In this paper, applying model...
We present an ab initio analysis with density functional theory for superconductors (SCDFT) to understand the superconducting mechanism of doped layered nitrides \beta-Li$_x$MNCl (M=Ti, Zr, and Hf). The current version SCDFT is based on Migdal-Eliashberg has been shown reproduce accurately experimental superconducting-transition temperatures Tc a wide range phonon-mediated superconductors. In case, however, our calculated Tc$\leq$4.3 K (M=Zr) $\leq$10.5 (M=Hf) are found be less than half Tc....
In valleytronics, bits of information would be stored using the so-called valley degrees freedom available in electronic band structures some semiconductors, such as transition metal dichalcogenides. The authors find emergent two-dimensional excitons well quantum confinement electrons to a single atomic layer bulk noncentrosymmetric MoS${}_{2}$ with $3R$ stacking. This stacking-engineered single-layer offers intriguing possibilities for dimension-dependent phenomena and robust carrier...
Superconductivity in novel bismuth-sulfur superconductors has attracted large research efforts, both experimental and theoretical, but a consensus on the nature of superconductivity these materials yet to be reached. Using density functional theory for superconductors, we study electron-phonon pairing mechanism ${\mathrm{LaO}}_{0.5}{\mathrm{F}}_{0.5}{\mathrm{BiS}}_{2}$. We first confirm presence commensurate charge wave instability, accordance with previous studies. recently developed...
We calculate the lattice dielectric function of strongly anharmonic rutile $\mathrm{TiO}_2$ from ab initio dynamics methods. Since an accurate calculation $\Gamma$ point phonons is essential for determining optical properties, we employ modified self-consistent approach, including third-order anharmonicity as well fourth-order anharmonicity. The resulting phonon frequencies and linewidths at much better agree with experimental measurements than those a perturbative approach. show that...
We review the recent progress in density functional theory for superconductors (SCDFT). Motivated by long-studied plasmon mechanism of superconductivity, we have constructed an exchange-correlation kernel entering SCDFT gap equation which includes effect. For case lithium under high pressures, show that effect substantially enhances transition temperature (Tc) cooperating with conventional phonon and results a better agreement between theoretical experimentally observed Tc. Our present...
We calculate superconducting gaps and quasiparticle density of states ${\mathrm{YNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ in the framework functional theory for superconductors to investigate origin highly anisotropic this material. Calculated phonon frequencies, states, transition temperature show good agreement with experimental results. From our calculation orbital character analysis, we establish that variation Fermi surface is key factor gap. Since electronic consist mainly Ni $3d$ orbitals...
We apply the density functional theory for superconductors based on local approximation (LDA) to alkali-doped fullerides ${A}_{3}$C${}_{60}$ with a face-centered-cubic structure. evaluate superconducting transition temperature (${T}_{\mathrm{c}}$) from first principles considering energy dependence of electron-phonon coupling, mass renormalization, and retardation effect. The calculated ${T}_{\mathrm{c}}=7.5$, 9.0, 15.7 K $A=\text{K}$, Rb, Cs are approximately 60% smaller than experimentally...
We present a study on the modification of electronic structure and hole-doping effect for layered dichalcogenide ${\mathrm{WSe}}_{2}$ with multivalley band structure, where Ta is doped W site along partial substitution Te its lighter counterpart Se. By means band-structure calculations specific-heat measurements, introduction theoretically experimentally found to change states in ${\mathrm{WSe}}_{2}$. While valence-band maximum located at $\ensuremath{\Gamma}$ point, raises bands $K$ point...