Large diamagnetic oscillatory relaxation above Tc in YBCO ceramics under non-equilibrium thermal conditions

Using a variant of the AC susceptibility method, we have demonstrated that under non-equilibrium thermal conditions, spontaneous incoherent local diamagnetic fluctuations could lead to large coherent oscillatory relaxation in YBCO ceramics above Tc. The probability and the amplitude of giant relaxation become maximum at ∼50% volume fraction of the diamagnetic state. Using the size of the largest synchronous cluster (determined from the amplitude of susceptibility relaxation) as coherence length (ξVG∼1.6±0.1 mm) together with the directly measured repetition period of the relaxation (τ∼10±1 s), the critical dynamic exponent has been calculated to be z=4.9±1. This value is in agreement with published vortex-glass exponent data.