Dynamic and Static Mechanical Measurements of Flux-Lattice Softening and Associated Hysteretic Depinning Dissipation Peak in YBa 2 Cu 3 O x Ceramic

We have studied flux-lattice dissipation in YBa 2 Cu 3 O x ceramic using a forced inverted torsional pendulum. Reversible restoring force variations during temperature sweep suggest that flux lines experience a “hard-soft” transition between 50 K and T c . Measurements of internal friction and modulus change as a function of the applied stress show a typical depinning behaviour. This dissipation peak during the temperature sweep is understood as a hysteretic depinning in which the critical force depends upon the penetration depth.