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Y. Muraoka

Publications and source records attributed to Y. Muraoka.

25 records · Page 2Linked to original sources
arXiv2005

High pressure effects on the superconductivity of beta-pyrochlore oxides AOs2O6

High pressure effects on the superconducting transitions of beta-pyrochlore superconductors AOs2O6 (A = Cs, Rb, K) are studied by measuring resistivity under high pressures up to 10 GPa. The superconducting transition temperature Tc first increases with increasing pressure in all the compounds and then exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa) and 10 K (0.6 GPa) for A = Cs, Rb and K, respectviely. Finally, the superconductivity is suppressed completely at a critical pressure near 7 GPa and 6 GPa for A = Rb and K and probably above 10 GPa for A = Cs. Characteristic changes in the coefficinet A of the T2 term in resistivity and residual resistivity are observed, both of which are synchronized with the corresponding change in Tc. It is suggested that electron correlations and certain quantum fluctuations play important roles in the occurrence or suppression of superconductivity in the beta-pyrochlore oxides.

cond-mat.supr-con↗
arXiv2004

New Pyrochlore Oxide Superconductor RbOs2O6

We report the discovery of a new pyrochlore oxide superconductor RbOs2O6. The compound crystallizes in the same beta-pyrochlore structure as the recently discovered superconductor KOs2O6, where Os atoms form a corner-sharing tetrahedral network called the pyrochlore lattice with Rb or K atoms in the cage. Resistivity, magnetic susceptibility and specific heat measurements on polycrystalline samples evidence a bulk superconductivity with Tc = 6.3 K.

cond-mat.supr-con↗
arXiv2003

Photoemission study of the metal-insulator transition in VO_2/TiO_2(001) : Evidence for strong electron-electron and electron-phonon interaction

We have made a detailed temperature-dependent photoemission study of VO_2/TiO_2(001) thin films, which show a metal-insulator transition at \sim 300 K. Clean surfaces were obtained by annealing the films in an oxygen atmosphere. Spectral weight transfer between the coherent and incoherent parts accompanying the metal-insulator transition was clearly observed. We also observed a hysteretic behavior of the spectra for heating-cooling cycles. We have derived the ``bulk'' spectrum of the metallic phase and found that it has a strong incoherent part. The width of the coherent part is comparable to that given by band-structure calculation in spite of its reduced spectral weight, indicating that the momentum dependence of the self-energy is significant. This is attributed to by ferromagnetic fluctuation arising from Hund's rule coupling between different d orbitals as originally proposed by Zylbersztejn and Mott. In the insulating phase, the width of the V 3d band shows strong temperature dependence. We attribute this to electron-phonon interaction and have reproduced it using the independent boson model with a very large coupling constant.

cond-mat.str-el↗
arXiv2002

Correlations and Semimetallic Behaviors in Pyrochlore Oxide Cd2Re2O7

Electronic properties of the metallic pyrochlore oxide Cd2Re2O7 are studied by means of electrical resistivity and Hall measurements. Semimetallic band structures are revealed as expected from band structure calculations. It is found that large changes in carrier density and mass occur at the structural phase transition at Ts1 = 200 K. A large mass enhancement is observed, particularly for the high-temperature phase with the ideal pyrochlore structure, suggesting that an anomalous correlation has an important effect on the itinerant electrons in the pyrochlore lattice.

cond-mat.str-el↗
arXiv2001

Structural Phase Transition in the Superconducting Pyrochlore Oxide Cd2Re2O7

We report a structural phase transition found at Ts = 200 K in a pyrochlore oxide Cd2Re2O7 which shows superconductivity at Tc = 1.0 K. X-ray diffractionexperiments indicate that the phase transition is of the second order, from a high-temperature phase with the ideal cubic pyrochlore structure (space group Fd-3m) to a low-temperature phase with another cubic structure (space group F-43m). It is accompanied by a dramatic change in the resistivity and magnetic susceptibility and thus must induce a significant change in the electronic structure of Cd2Re2O7.

cond-mat.supr-con↗
arXiv2001

Superconductivity at 1 K in Cd2Re2O7

We report the first pyrochlore oxide superconductor Cd2Re2O7. Resistivity,magnetic susceptibility,and specific heat measurements on single crystals evidence a bulk superconductivity at 1 K. Another phase transition found at 200 K suggests that a peculiar electronic structure lies behind the superconductivity.

cond-mat.supr-con↗