Mass enhancement, correlations, and strong-coupling superconductivity in the β-pyrochlore KOs2O6
M. Brühwiler, S. M. Kazakov, J. Karpinski, B. Batlogg
DOI 10.1103/PhysRevB.73.094518 · Physical Review B
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Abstract
To assess electron correlation and electron-phonon coupling in the recently discovered β-pyrochlores KOs2O6 and RbOs2O6, we have performed specific heat measurements in magnetic fields up to 14T. We present data from high-quality single-crystalline KOs2O6, showing that KOs2O6 is a strong-coupling superconductor with a coupling parameter λep≈1.0–1.6 (RbOs2O6: λep≈1). The estimated Sommerfeld coefficient of KOs2O6, γ=76–110mJ∕molK2, is twice that of RbOs2O6 (γ=44mJ∕molK2). Using strong-coupling corrections, we extract useful thermodynamic parameters of KOs2O6. Quantifying λep allows us to determine the mass enhancement over the calculated band electronic density of states. A significant contribution in addition to the electron-phonon term of λc=1.7–4.3 is deduced. In an effort to understand the origin of the enhancement mechanism, we also investigate an unusual energetically low-lying phonon. There are three phonon modes per RbOs2O6, suggestive of the phonon source being the rattling motion of the alkali-metal ion. This dynamic instability of the alkali-metal ions causes large scattering of the charge carriers which shows up in an unusual temperature dependence of the electrical resistivity.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| KOs2O6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 9.5 | Pressure not reported | unknown |
| RbOs2O6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 6.4 | Pressure not reported | unknown |
| CsOs2O6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 3.3 | Pressure not reported | unknown |
| Cd2Re2O7 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
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