Extremely strong-coupling superconductivity and anomalous lattice properties in the beta-pyrochlore oxide KOs2O6

Abstract

Superconducting and normal-state properties of the beta-pyrochlore oxide KOs2O6 are studied by means of thermodynamic and transport measurements. It is shown that the superconductivity is of conventional s-wave type and lies in the extremely strong-coupling regime. Specific heat and resistivity measurements reveal that there are characteristic low-energy phonons that give rise to unusual scattering of carriers due to strong electron-phonon interactions. The entity of the low-energy phonons is ascribed to the heavy rattling of the K ion confined in an oversized cage made of OsO6 octahedra. It is suggested that this electron-rattler coupling mediates the Cooper pairing, resulting in the extremely strong-coupling superconductivity.

17 pages (only 4 pages included here. go to http://hiroi.issp.u-tokyo.ac.jp/Published%20papers/K-SC6.pdf for full pages), to be published in PRB

References in corpus (6)

• Mass enhancement, correlations, and strong coupling superconductivity in the beta-pyrochlore KOs2O6
• Crystal growth, structural studies and superconducting properties of beta-pyrochlore KOs2O6
• NMR Observation of Rattling Phonons in the Pyrochlore Superconductor KOs2O6
• Thermal Conductivity of the Pyrochlore Superconductor KOs2O6: Strong Electron Correlations and Fully Gapped Superconductivity
• Uncommonly High Upper Critical Field in the Superconducting KOs${}_2$O${}_6$ Pyrochlore
• Anomalous Flux Pinning in ?-Pyrochlore Oxide Superconductor KOs2O6

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• Phonon density of states, anharmonicity, electron-phonon coupling and possible multigap superconductivity in the clathrate superconductors Ba8Si46 and Ba24Si100: Why is Tc different in these two compounds?
• Superconducting Transition in the $\beta$-Pyrochlore AOs${}_2$O${}_6$ (A=Cs, Rb, K) under Pressure
• A Possible Phase Transition in beta-pyrochlore Compounds
• Vortex Redistribution below the First-Order Transition Temperature in the β-Pyrochlore Superconductor KOs_2O_6
• Scanning Tunneling Spectroscopy in the Superconducting State and Vortex Cores of the beta-pyrochlore KOs2O6
• Theoretical study of NMR relaxation due to rattling phonons
• Magnetic and charge transport properties of the Na-based Os oxide pyrochlore
• Structural and Superconducting Properties of RbOs2O6 Single Crystals
• Green's function of fully anharmonic lattice vibration