arXiv subjects

R. Tamura

Publications and source records attributed to R. Tamura.

3 recordsLinked to original sources

arXiv2025

Simultaneous probes of pseudogap and disorder by hard x-ray photoemission applied for a candidate thermoelectric Al-Pd-Ru quasicrystal

The bulk electronic structure of Al-Pd-Ru quasicrystal (QC) have been investigated by hard X-ray photoemission spectroscopy (HAXPES). We have found an intrinsic pseudogap structure in which the spectral weight in the vicinity of the Fermi level (E_F) is remarkably suppressed at any photon energy. The valence-band HAXPES spectra and the asymmetry of the core-level peaks indicate a contribution of the Al sites to the electronic structure in the vicinity of E_F with less contributions from the Pd and Ru sites. The disorder effects are found in the core-level lineshapes of the Al-Pd-Ru QC, of which the widths are much broader than those of the other reference crystalline solids with less disorder.

cond-mat.mtrl-sci↗

arXiv2010

Structural Modification and Metamagnetic Anomaly in the Ordered State of CeOs2Al10

A caged compound CeOs2Al10, crystallizing in the orthorhombic YbFe2Al10-type structure, undergoes a mysterious phase transition at T_0=29 K. We report the results of electron diffraction, magnetization, and magnetoresistance for single crystals. Superlattice reflections characterized by a wave vector q = (0, -2/3, 2/3) observed at 15 K indicate a structural modification in the ordered state. Activation-type behavior of the electrical resistivity along the three principal axes below 50 K suggests gap opening in the conduction band. The magnetic susceptibility χ= M/B is highly anisotropic, χ_a>χ_c>χ_b, all of which sharply decrease on cooling below T_0. Furthermore, a metamagnetic anomaly in the magnetization and a step in the magnetoresistance occur at B=6-8 T only when the magnetic field is applied parallel to the orthorhombic c axis. However, T_0 hardly changes under magnetic fields up to 14 T, irrespective of the field direction. By using these data, we present a B-T phase diagram and discuss several scenarios for the mysterious transition.

cond-mat.str-el↗

arXiv2004

Electronic states in 1/1 Cd6Yb and 1/1 Cd6Ca: Relativistic, correlation, and structural effects

The electronic structure of the rational approximants 1/1 Cd6Yb and 1/1 Cd6Ca to the stable icosahedral CdYb and CdCa quasicrystals is studied by the full-potential linear augmented plane wave method. A comparison is made between several structural models. We show that the (relativistic) spin-orbit (SO) interaction and electronic correlations that are not described by the usual local density approximation, are essential for an accurate description of the electronic structure. In particular, we show that the SO interaction is responsible for a splitting of the Cd-4d and Yb-4f peaks, and that the experimental peak positions can be reproduced by including a Hubbard U term in the Hamiltonian [U(Cd) = 5.6 eV, U(Yb) = 3.1 eV]. Our results show very good agreement with a photo-emission (PE) spectrum of 1/1 Cd6Yb [R. Tamura, Y. Murao, S. Takeuchi, T. Kiss, T. Yokoya, and S. Shin, Phys. Rev. B 65, 224207 (2002)] and a 350 eV PE spectrum of 1/1 Cd6Ca, which we present in this paper. Without the relativistic and correlation effects even a qualitative agreement with the PE spectra cannot be achieved.

cond-mat.other↗