Smearing origin of zero-bias conductance peak in Ag-SiO-Bi-2212 planar tunnel junctions: influence of diffusive normal metal verified with the circuit theory

TL;DR

This paper analyzes the origin of zero-bias conductance peaks in high-Tc superconductor junctions using circuit theory, revealing that midgap Andreev resonant states and diffusive normal metal effects explain the spectral features without additional broadening factors.

Contribution

It introduces a simplified circuit theory approach for d-wave superconductors to explain ZBCP features in tunnel junctions, emphasizing the roles of MARS and DN resistance.

Findings

Spectral features of ZBCP are well explained by circuit theory.

The analysis excludes the need for Dynes's broadening factor.

Results are consistent with extended circuit theory for d-wave systems.

Abstract

We propose a new approach of smearing origins of a zero-bias conductance peak (ZBCP) in high-Tc superconductor tunnel junctions through the analysis based on the circuit theory for a d-wave pairing symmetry. The circuit theory has been recently developed from conventional superconductors to unconventional superconductors. The ZBCP frequently appears in line shapes for this theory, in which the total resistance was constructed by taking account of the effects between a d-wave superconductor and a diffusive normal metal (DN) at a junction interface, including the midgap Andreev resonant states (MARS), the coherent Andreev reflection (CAR) and the proximity effect. Therefore, we have analyzed experimental spectra with the ZBCP of Ag-SiO-Bi-2212 planar tunnel junctions for the {110}-oriented direction by using a simplified formula of the circuit theory for d-wave superconductors. The fitting results reveal that the spectral features of the ZBCP are well explained by the circuit theory not only excluding the Dynes's broadening factor but also considering only the MARS and the DN resistance. Thus, the ZBCP behaviors are understood to be consistent with those of recent studies on the circuit theory extended to the systems containing d-wave superconductor tunnel junctions.