Evidence of s-Wave Subdominant Order Parameter in YBCO from Break Junction Tunneling Spectra

TL;DR

This study provides evidence for a subdominant s-wave component in YBCO by analyzing tunneling spectra, zero-bias conductance peak splitting, and Josephson current behavior, indicating a mixed order parameter at low temperatures.

Contribution

It demonstrates the presence of a subdominant s-wave order parameter in YBCO through tunneling spectra and Josephson current measurements, aligning with theoretical predictions.

Findings

Deep ZBCP splitting starts below 20-30K

Magnetic field significantly depresses ZBCP splitting

Josephson current saturates at low temperatures, indicating mixed order parameter

Abstract

The tunneling spectra of YBa2Cu3O7 break-junctions have been investigated for the tunneling direction close to the node one. 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<20-30K is in agreement with the theory for the dx2-y2+-is order parameter [Y. Tanuma, Y. Tanaka, and S. Kashiwaya, Phys. Rev. B 64, 214519 (2001)]. The low (0.04T) magnetic field depresses significantly such splitting. The 1/T temperature dependence of maximum Josephson current goes to saturation at T<Ts also confirming the mixed order parameter formation.