On the Zero-Bias Conductance Peak in the Tunneling Spectroscopy

TL;DR

This paper develops a generalized image method combined with Keldysh-Green's functions to analyze tunneling spectroscopy in hybrid systems, revealing conditions for zero-bias conductance peaks and their behavior under various states and symmetries.

Contribution

It introduces a unified approach to study ZBCP in diverse hybrid systems, linking particle-hole pairing states to a simple 1D model and identifying broken reflection symmetry as essential for ZBCP.

Findings

ZBCP evolution with doping in ND junctions

Splitting of ZBCP in magnetic fields

Broken reflection symmetry is necessary for ZBCP

Abstract

A generalized method of image, incorporated with the non-equilibrium Keldysh-Green's function formalism, is employed to investigate the tunneling spectroscopy of hybrid systems in the configuration of planar junction. In particular, tunneling spectroscopies of several hybrid systems that exhibit zero-bias conductance peaks (ZBCP) are examined. The well-known metal--d-wave superconductor (ND) junction is first examined in detail. Both the evolution of the ZBCP versus doping and the splitting of the ZBCP in magnetic fields are computed in the framework of the slave-boson mean field theory. Further extension of our method to analyze other states shows that states with particle-hole pairing, such as d-density wave and graphene sheet, are all equivalent to a simple 1D model, which at the same time also describes the polyacetylene. We provide the criteria for the emergence of ZBCP. In particular, broken reflection symmetry at the microscopic level is shown to be a necessary condition for ZBCP to occur.