Masaki Uchida 교수

We report strain engineering of superconductivity in RuO$_2$ singlecrystalline films, which are epitaxially grown on rutile TiO$_2$ and MgF$_2$ substrates with various crystal orientations. Systematic mappings between the superconducting transition temperature and the lattice parameters reveal that shortening of specific ruthenium-oxygen bonds is a common feature among the superconducting RuO$_2$ films. Ab initio calculations of electronic and phononic structures for the strained RuO$_2$ films s

We have investigated charge dynamics and electronic structures for single crystals of metallic layered nickelates, ${R}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{NiO}}_{4}$ ($R=\mathrm{Nd},\mathrm{Eu}$), isostructural to ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$. Angle-resolved photoemission spectroscopy on the barely metallic ${\mathrm{Eu}}_{0.9}{\mathrm{Sr}}_{1.1}{\mathrm{NiO}}_{4}$ ($R=\mathrm{Eu}$, $x=1.1$) has revealed a large hole surface of ${x}^{2}\ensuremat

The recent discovery of topological Dirac semimetals (DSMs) has provoked intense curiosity not only regarding Weyl physics in solids but also about topological phase transitions originating from DSMs. One specific area of interest is controlling the dimensionality to realize two-dimensional quantum phases such as quantum Hall and quantum spin Hall states. For investigating these phases, the Fermi level is a key controlling parameter. From this perspective, we report the carrier density control o

${\mathrm{Ba}}_{3}{\mathrm{Mn}}_{2}{\mathrm{O}}_{8}$ is an $S=1$ coupled spin dimer system with a gapped ground state. The magnetization process of this compound has been measured up to 50 T at 0.65 K. Magnetization plateaus were clearly observed at zero and at half of the saturation magnetization. The excitation gap was estimated as $\ensuremath{\Delta}{/k}_{\mathrm{B}}=12.3 \mathrm{K}.$ The magnetization curve was analyzed and the spin structure in the field-induced ordered state was discussed

Charge dynamics of (Ti1-xVx)2O3 with x=0-0.06 has been investigated by measurements of charge transport and optical conductivity spectra in a wide temperature range of 2-600 K with the focus on the thermally and doping induced insulator-metal transitions (IMTs). The optical conductivity peaks for the interband transitions in the 3d t_{2g} manifold are observed in both the insulating and metallic states, while their large variation (by approximately 0.4 eV) with change of temperature and doping l

We report the growth of superconducting Sr2RuO4 films by oxide molecular beam epitaxy (MBE). Careful tuning of the Ru flux with an electron beam evaporator enables us to optimize growth conditions including the Ru/Sr flux ratio and also to investigate stoichiometry effects on the structural and transport properties. The highest onset transition temperature of about 1.1 K is observed for films grown in a slightly Ru-rich flux condition in order to suppress Ru deficiency. The realization of superc

We report a systematic investigation on the high-temperature thermoelectric response in a typical filling-control Mott transition system La${}_{1\ensuremath{-}x}$Sr${}_{x}$VO${}_{3}$. In the vicinity of the Mott transition, incoherent charge transport appears with increasing temperature and the thermopower undergoes two essential crossovers, asymptotically approaching the limit values expected from the entropy consideration, known as the Heikes formula. By comparison with the results of the dyna

We employ molecular beam epitaxy to stabilize ${\mathrm{Ba}}_{2}{\mathrm{IrO}}_{4}$ thin films and utilize in situ angle-resolved photoemission spectroscopy to investigate the evolution of its electronic structure through the N\'eel temperature ${T}_{\mathrm{N}}$. Our measurements indicate that dispersions of the relativistic ${J}_{\mathrm{eff}}=1/2$ and 3/2 bands exhibit an unusual dichotomy in their behavior through the N\'eel transition. Although the charge gap survives into the paramagnetic

Rapid progress of quantum transport study in topological Dirac semimetal, including observations of quantum Hall effect in two-dimensional (2D) Cd3As2 samples, has uncovered even more interesting quantum transport properties in high-quality and three-dimensional (3D) samples. However, such 3D Cd3As2 films with low carrier density and high electron mobility have been hardly obtained. Here, we report the growth and characterization of 3D thick Cd3As2 films adopting molecular beam epitaxy. The high

We report an above-room-temperature ferromagnetic state realized in a proximitized Dirac semimetal, which is fabricated by growing typical Dirac semimetal ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ films on a ferromagnetic garnet with strong perpendicular magnetization. Observed anomalous Hall conductivity with substantially large Hall angles is found to be almost proportional to magnetization and opposite in sign to it. Theoretical calculations based on first-principles electronic structure also demo

Nonsymmorphic materials, which possess special symmetry operations (screw rotation, glide mirror), have been theoretically reexamined in recent years for possible novel quantum phases or electronic functions derived from the symmetry requirements. Here, the authors demonstrate that in the typical nonsymmorphic material IrO${}_{2}$, the type of charge carrier (electron or hole) is strongly dependent on the crystal orientation and capable of being switched by a magnetic field. This remarkable effe

While anomalous Hall effect (AHE) has been extensively studied in the past, efforts for realizing large Hall response have been mainly limited within intrinsic mechanism. Lately, however, a theory of extrinsic mechanism has predicted that magnetic scattering by spin cluster can induce large AHE even above magnetic ordering temperature, particularly in magnetic semiconductors with low carrier density, strong exchange coupling, and finite spin chirality. Here, we find out a new magnetic semiconduc