Peculiarities of the temperature behavior of the pyroelectric effect in YBCO thin films in the vicinity of the superconducting transition

Abstract

Light induced pyroelectric effect in superconducting YBCO thin films with different morphologies was observed. Measurements of the temperature dependence of the pyroelectric voltage in the vicinity of Tc revealed such peculiarities of its behavior as a pronounced peak in the voltage just above Tc and the sign voltage reversal at Tm (110 – 150 K) dependent on sample properties. The strong influence of the external magnetic field on the peak height was found, although, as opposed to superconducting transition, no appreciable temperature shift of the peak was observed. Joint consideration of data on temperature and magnetic behavior of the pyroelectric voltage point to that the spontaneous polarization Ps dramatically changes near Tc but exists in superconducting phase too. The existence of macroscopic Ps and its discontinuity near Tc was ascribed to the local noncentrosymmetry of the YBCO structure and some its transformation just above Tc