High-pressure resistivity measurements on the β-pyrochlore oxide KOs2O6

High-pressure resistivity measurements are performed on a high-quality single crystal of the β -pyrochlore oxide KOs2O6 in the pressure range of 1.0 to 5.0 GPa. The superconducting transition temperature T c increases slightly from 9.6 K at ambient pressure to 9.8 K at 1.0 GPa, decreases gradually with increasing pressure, and suddenly drops from 6.5 K to 3.2 K across P s = 3.6 GPa . The drop of T c at P s is likely to be related to a change in the rattling vibration associated with a symmetry-breaking structural transition.