CHARACTERIZATION OF THE SUPERCONDUCTING TRANSITION IN SINGLE-CRYSTAL URU2SI2

To investigate the nature of the superconducting transition in URu2Si2 we have made careful studies of the specific heat on oriented samples cut from a high-quality single crystal. Our high-resolution a.c.-specific-heat experiments establish the existence of only one sharp superconducting transition. Measurements in applied fields of up to 5 Tesla show that fields along both the a and c axes induce no splitting of the transition. From these C(p)(H) results the upper critical field can be obtained, elucidating for the first time the bulk behaviour of H(c2)(T). The large anisotropy (H(c2, a) >> H(c2, c)) and the small region of positive curvature near T(c) for H parallel-to a agree with the results obtained from resistivity and a.c.-susceptibility measurements.