Direct Transition from Bose Glass to Normal State in the (K,Ba)BiO3 Superconductor

International audienceThe introduction of columnar defects in K; Ba BiO3 single crystals shifts both the irreversibility and thermodynamic transition lines, respectively, deduced from ac susceptibility (and/or transport) and specific heat measurements, upwards. This shift can be attributed to the defect-induced decrease of the difference ( F) between the free energies in the superconducting and the normal states, assuming that the position of the superconducting transition is given by the condition j Fj kBT= 3. This criterion also perfectly reproduces the influence of the angle between the tracks and the external field. This result suggests that no vortex liquid phase exists in this system