Constraints on the temperature dependence of the magnetic penetration depth of superconducting Bi2Sr2CaCu2O8+x from measurements of the low-temperature specific heat

Abstract

We have measured the low-temperature (2"10 K) specific heat of polycrystalline Bi2Sr2CaCu2O8+x in zero applied field and in an applied magnetic field of 1 T. We find no field-induced enhancement of the specific heat, to within the 1% resolution of our calorimeter, in a field of 1 T up to 10 K, in contrast to the YBa2Cu3O7- system. The results suggest that the enhancements which have been observed in the specific heat result from a temperature dependence of the pinning of vortices in the mixed state. In analyzing our data, we use a model for the enhancement of the specific heat, and find quantitative agreement. Using this model, we place constraints on the allowed temperature dependence of the ab-plane magnetic penetration depth. © 1992 The American Physical Society.