Investigations of the zero-field ( a,b)-plane conductivity of YBa 2Cu 3O 7−δ near the critical temperature

Abstract

The resistive transition R( T) and the current–voltage characteristics ( I–V) in the range 10 −9–10 −6 V and close to the critical temperature ( T c) were measured in a single-grain of melt-textured YBa 2Cu 3O 7−δ (YBCO) and in a detwinned YBCO single-crystal, with the transport current parallel to the ( a,b) planes and in zero external magnetic field using a SQUID picovoltmeter. In the case of the melt-textured sample, we measured the I–V curves also at higher levels of dissipation. For T< T c, we interpreted the lower part of the I–V curves in the framework of the Jensen–Minnhagen model of current-induced unbinding of thermally-created vortex–antivortex pairs, which leads to V∝ I( I− I c1) a−1 . Our results confirm a recently proposed current–temperature ( I–T) phase diagram by S.W. Pierson. In addition, we determined for the first time the dependence of the characteristic (unbinding) current I c1 with t=1− T/ T c for temperatures very close to T c and low transport currents.