Origin of the Electron-Hole Asymmetry in the Scanning Tunneling Spectrum of the High-Temperature Bi 2 Sr 2 CaCu

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 Bi2Sr2CaCu2O8þ (Bi2212) show clearly that the tunneling process strongly modifies the STS spectrum from the local density of states of the dx2 y orbital of Cu. The dominant tunneling channel to the surface Bi involves the dx2 y 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 dz2 and other orbitals to the tunneling current.