Anisotropic enhancement of superconductivity in heavy-ion irradiated (K, Ba)BiO3

Phys Rev Lett. 2003 Jan 24;90(3):037004. doi: 10.1103/PhysRevLett.90.037004. Epub 2003 Jan 23.

Abstract

We have measured the specific heat, resistivity, and ac susceptibility of (K,Ba)BiO3 single crystals before and after introduction of either point or columnar defects by electron (EI) or heavy-ion irradiation (HII). While the magnetic field dependence of these properties remains mainly unaffected by EI, the irreversibility line and the location of the specific heat anomaly are both shifted up in temperature after HII. The shift is apparent only if the magnetic field is applied parallel to the ion tracks. For perpendicularly applied fields, both lines lie at the same field as in the pristine sample. These experiments call the nature of the vortex liquid state into question.