Origin of the Electron-Hole Asymmetry in the Scanning Tunneling Spectrum of the High-Temperature Bi2Sr2CaCu2O8+δ Superconductor

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+delta (Bi2212) show clearly that the tunneling process strongly modifies the STS spectrum from the local density of states 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 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(z)(2) and other orbitals to the tunneling current.