Origin of electron-hole asymmetry in the scanning tunneling spectrum of $Bi_2Sr_2CaCu_2O_{8+\delta}$

TL;DR

This paper presents a material-specific theoretical model for scanning tunneling spectroscopy of high-temperature superconductor Bi2212, revealing how tunneling processes cause electron-hole asymmetry in the spectrum.

Contribution

It introduces a novel theoretical framework that accounts for orbital contributions and tunneling effects, explaining observed asymmetries in STS spectra of Bi2212.

Findings

Tunneling modifies the local density of states in the spectrum.

Electron-hole asymmetry arises from Cu $d_{z^2}$ and other orbitals.

The model aligns with experimental observations of spectral asymmetry.

Abstract

We have developed a material specific theoretical framework for modelling scanning tunneling spectroscopy (STS) of high temperature superconducting materials in the normal as well as the superconducting state. Results for $Bi_2Sr_2CaCu_2O_{8+\delta}$ (Bi2212) show clearly that the tunneling process strongly modifies the STS spectrum from the local density of states (LDOS) of the $d_{x^2-y^2}$ orbital of Cu. The dominant tunneling channel to the surface Bi involves the $d_{x^2-y^2}$ orbitals of the four neighbouring Cu atoms. In accord with experimental observations, the computed spectrum displays a remarkable asymmetry between the processes of electron injection and extraction, which arises from contributions of Cu $d_{z^2}$ and other orbitals to the tunneling current.