Substitutional doping of Cu in diamond: Mott physics with p orbitals

Discovery of superconductivity in the impurity band formed by heavy doping of boron into diamond (C:B) as well as doping of boron into silicon (Si:B) has provided a rout for the possibility of new families of superconducting materials. Motivated by the special role played by copper atoms in high temperature superconducting materials where essentially Cu d orbitals are responsible for a variety of correlation induced phases, in this paper we investigate the effect of substitutional doping of Cu into diamond. Our extensive first principle calculations based on density functional theory which are averaged over various geometries indicate the formation of a mid-gap band, which mainly arises from the t 2 g and 4p states of Cu. For impurity concentrations of more than ~1%, the effect of 2p bands of neighboring carbon atoms can be ignored. Based on our detailed analysis, we suggest a two band model for the mid-gap states consisting of a quarter-filled hole like t 2 g band, and a half-filled band of 4p states. Increasing the concentration of the Cu impurity beyond ~5%, completely closes the spectral gap of the host diamond. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010