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

TL;DR

This study explores how substituting copper into diamond creates new electronic states, potentially leading to novel superconducting phases driven by strong electron correlations involving Cu $p$ orbitals.

Contribution

It provides the first detailed first-principles analysis of Cu doping in diamond, revealing the formation of mid-gap bands and proposing a two-band model for correlated electronic states.

Findings

Mid-gap bands mainly from Cu $t_{2g}$ and $4p$ states.

Spectral gap closes at impurity concentrations above 5%.

Proposes a two-band model for the impurity states.

Abstract

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 averaged over various geometries based on density functional theory, indicates the formation of a mid-gap band, which mainly arises from the $t_{2g}$ and $4p$ states of Cu. For impurity concentrations of more than $\sim 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 $t_{2g}$ band, and a half-filled band of $4p$ states. Increasing the concentration of the Cu impurity beyond $\sim 5%, completely closes the spectral gap of the host diamond.