First-order melting transition observed from resistivity measurements in ultra-pure YBa 2Cu 3O 7− δ single crystals with high twin boundary density

Abstract

R( T) measurements have been performed on optimally and overdoped heavily twinned high-purity YBa 2Cu 3O 7− δ single crystals, under a magnetic field B oriented parallel to the twin boundary planes ( B‖ c). The characteristic feature attributed to the flux line lattice melting transition has been observed in the overdoped case for B≥5 T. The first-order transition was not found in the optimally doped sample, even when B was tilted with respect to the c-axis. Differences between these samples are discussed.