Anomalous Pressure Dependence of the Superconducting Transition Temperature of β-Pyrochlore AOs_2O_6 Oxides

摘要

High-pressure effects on the superconducting transitions of β-pyrochlore oxide superconductors AOs_2O_6 (A = Cs, Rb, K) are studied by measuring resistivity under high pressures up to 10 GPa. The superconducting transition temperature T_c first increases with increasing pressure in every compound 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, respectively. 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 coefficient A of the T~2 term in resistivity and residual resistivity are observed, both of which are synchronized with the corresponding change in T_c.