Superconducting transition in the β-pyrochlore AOs2O6 (A = Cs, Rb, K) under pressure

Pressure dependence of superconducting transition temperature T, has been determined through the DC magnetic measurements under pressure up to P = 10 GPa for beta-pyrochlore oxides AOs(2)O(6) with A = Cs (T-c = 3.3 K), Rb (6.3 K), and K (9.6 K). Both for A = Rb and Cs, T-c increases with increasing P and shows a saturation at T-m similar to 8.8 K, which is considered as the upper limit of T, inherent in AOs(2)O(6). In contrast, the T-c-P curve for KOs2O6 shows a sharp maximum of similar to 10 K at P similar to 0.5 GPa, and T-c is higher than T-cm for 0 <= P <= 1.5 GPa, suggesting the enhanced superconductivity due to the rattling of K ions.