Observation of irreversible to reversible transition in Tl 2Ba 2Ca 2Cu 3O x by magnetic field dependent microwave absorption

Abstract

The magnetic field dependence of the microwave absorption due to flux motion has been measured at several temperatures in the superconducting state of Tl 2Ba 2Ca 2Cu 3O x . At a given temperature there are two magnetic field regions in which the microwave absorption displays a different functional dependence on the magnetic field strength and there is a definite magnetic field, B′, separating the two regions. The lower field region is associated with the dynamics of flux motion in the irreversible, strong flux pinning regime, and the upper region with flux motion in the reversible fluid phase. The microwave absorption is shown to display a hysteresis in the field direction below B′ but not above it. A measurement of the temperature dependence of the transition magnetic field, B′, between the two regions allows a determination of the H- T irreversibility line for surface melting of the vortex solid.