Thermodynamics of a heavy-ion-irradiated superconductor: The zero-field transition

Specific heat measurements show that the introduction of amorphous columnar defects considerably affects the transition from the normal to the superconducting state in zero magnetic field. Experimental results are compared to numerical simulations of the three-dimensional XY model for both the pure system and the system containing random columnar disorder. The numerics reproduce the salient features of experiment, showing in particular that the specific heat peak changes from cusplike to smoothly rounded when columnar defects are added. By considering the specific heat critical exponent , we argue that such behavior is consistent with recent numerical work A. Vestergren et al., Phys. Rev. B 70, 054508 2004 showing that the introduction of columnar defects changes the universality class of the transition.