Tunneling into Current-Carrying Surface States of High T$_c$ Superconductors

TL;DR

This paper presents theoretical analysis of tunneling conductance in high-Tc d-wave superconductors, predicting surface states, ZBCP splitting, and surface currents, with comparisons to experimental data on Cu/YBCO junctions.

Contribution

It introduces a model explaining ZBCP splitting and surface currents in high-Tc superconductors, aligning theory with recent experiments.

Findings

Surface bound states exist below the maximum gap.

Zero-bias conductance peak splits due to sub-dominant order parameter.

Magnetic fields cause voltage splitting of ZBCP proportional to field strength.

Abstract

Theoretical results for the ab-plane tunneling conductance in the d-wave model for high Tc superconductors are presented. The d-wave model predicts surface bound states below the maximum gap. A sub-dominant order parameter, stabilized by the surface, leads to a splitting of the zero-bias conductance peak (ZBCP) in zero external field and to spontaneous surface currents. In a magnetic field screening currents shift the quasiparticle bound state spectrum and lead to a voltage splitting of the ZBCP that is linear in H at low fields, and saturates at a pairbreaking critical field of order 3 Tesla. Comparisons with recent experimental results on Cu/YBCO junctions are presented.