Non-linearity of a thermodynamic instability in high-Tc superconductors

Submitting high-T-c superconductors to the effect of a large temperature gradient and a thermal pulse, damped oscillation of d.c. and a.c. voltages is detected on the samples. It represents the appearance of a novel type of thermodynamic instability, which manifests itself in temporal fluctuation of normal-superconducting and superconducting-normal transitions of coherent domains, depending on the local structural properties of the material at a given temperature and magnetic field. The strong non-linearity of this phenomenon is attributed mainly to thermodynamic cross-effects, taking into account the dissipation of the vortex motion, too. General motion equations of irreversible thermodynamics characterize correctly the decaying behaviour of the disturbed state.