Comparative AC susceptibility and resistivity studies of the vortex lattice melting transition in detwinned YBa 2Cu 3O 7− δ single crystals

Abstract

We have studied the transition from the vortex liquid to the vortex solid state in clean, detwinned YBa 2Cu 3O 7− δ single crystals in fields up to 12 T using AC susceptibility and resistivity measurements. For μ 0 H<7 T a sharp drop in the resistivity at a temperature T m (which has been shown to be a signature of a first order phase transition [1, 2]) was found to be accompanied by an AC field independent abrupt onset of both χ′ and χ″ components. The AC susceptibility data suggest that just below T m there is a transition region where the liquid and solid phases coexist. The width of the transition region was found to be sample dependent and can be related to structural inhomogeneity. Above the multicritical field μ 0 H mc=7 T simultaneous broadening of both the ρ( T) drop and the χ″( T) onset show that the first order melting transition is suppressed.