Disorder and non-linear magnetic response of high Tc superconductors

Abstract

International audienceWe measure the low frequency magnetic response of YBa2Cu3O6.7Fx (0 <= x< 0.2) ceramics in a wide range of a.c. fields (10-7 T <= µ0H0 <= 10-4 T). When changing the amount of disorder (varying x) on the microscopic level we find the same non linear response with field amplitude H0 as in granular conventional superconductors. The real part of the susceptibility appears as a universal function of H1(T)/H0 where H1(T) is the field of first flux penetration. The power law dependence found for H1(T) can be understood in the framework of the coherence transition of granular superconductors with random couplings