Non-isothermal conditions and the scaling of activation energy in high temperature superconductors

Recent experimental data on the HTSC compound HgBa2CaCu2O6+δ suggest that the temperature scaling which follows Up(T)∼(1-T/Tc)m, m=1.10±0.04, and the magnetic field scaling of the activation energy might not be correlated. Furthermore, the dependence of the activation energy on the magnetic field given by Up∝H-1 is not directly associated with the dimensionality of the material. We propose a model to explain this behavior in terms of the magnetothermal effects and vortex excitations associated with thermal gradients. In particular, these effects can be substantial due to the high transition temperatures of the HgBa2CaCu2O6+δ system. The analysis reproduces the general dependence of the activation energy on both the temperature and magnetic field confirming the importance of the vortex excitations for the activation energies. (orig.)