Evidence of a s-wave subdominant order parameter in YBa₂Cu₃O₇₋δ from break-junction tunneling spectra

Abstract

The tunneling spectra of YBa₂Cu₃O₇₋δ break-junctions have been investigated for the tunneling direction close to the node one. The behavior of the zero-bias conductance peak (ZBCP) and Josephson current have been studied with temperature and magnetic field. The observed deep splitting of ZBCP which starts at TS<20–30 K is in agreement with the theory for the dx²–y²± is order parameter [Y. Tanuma, Y. Tanaka, and S. Kashiwaya, Phys. Rev. B64, 214519 (2001)]. We also observed that a low (0.04 T) magnetic field significantly depresses such splitting. The 1/T temperature dependence of maximum Josephson current that goes to saturation at T<TS also confirms the mixed order parameter formation.