FIELD-DEPENDENCE OF SPECIFIC-HEAT IN THE MIXED-STATE OF YBA2CU3O7-DELTA

The non-linear behavior of the change in specific heat Delta C versus the applied field B-a of YBa2Cu3O7-delta near the transition temperatu re T-c is explained qualitatively by incorporating the overlap of vort ices in the London model. The overlap of vortices increases the magnet ic interaction range lambda by a factor 1/root 1-b, where b = B-a/B-c2 . Based on this analysis, it is shown that the Delta C peak shifts to lower temperature with magnetic field. This effect is more pronounced for B-a parallel to the c-axis than that for B-a perpendicular to the c-axis. The shift of the Delta C peak with respect to the bare transit ion temperature T-c(0) varies linearly with B-a(1/2v) as the upper cri tical field varies as (1-t)(2v), where t = T/T-c. It is also found tha t both the width and the shift have the same field dependence as predi cted in the finite-size scaling model.