Origin of the electron-hole asymmetry in the scanning tunneling spectrum of the high-temperature Bi₂Sr₂CaCu₂O₈+δ superconductor

Jouko Nieminen, Tampere University of Technology
Hsin Lin, Northeastern University
R. S. Markiewicz, Northeastern University
A. Bansil, Northeastern University

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Originally published in Physical Review Letters v.102 (2009): 037001. DOI: 10.1103/PhysRevLett.102.037001

Abstract

We have developed a material specific theoretical framework for modeling scanning tunneling spectroscopy (STS) of high-temperature superconducting materials in the normal as well as the superconducting state. Results for Bi₂Sr₂CaCu₂O₈₊_δ (Bi2212) show clearly that the tunneling process strongly modifies the STS spectrum from the local density of states of the dₓ²₋_y² orbital of Cu. The dominant tunneling channel to the surface Bi involves the dₓ²₋_y² orbitals of the four neighboring 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_z² and other orbitals to the tunneling current.