Resonating Valence Bond Mechanism of Impurity Band Superconductivity in Diamond

Abstract

Superconductivity in an uncompensated boron doped diamond, a very recent observation, is strikingly close to an earlier observation of Anderson-Mott insulator to metal transition, prompting us to suggest an electron correlation driven superconductivity in an impurity band. Random coulomb potential remove a three fold orbital degeneracy of boron acceptor states, resulting in an effective single, narrow, tight binding and half filled band of holes. Singlet coupling between spins of neighboring neutral acceptors $B^0-B^0$ is the seed of pairing. Across the insulator to metal transition, a small and equal fraction of charged $B^+$ and $B^-$ states (free carriers) get spontaneously generated and delocalize. Thereupon neutral singlets resonate and get charged resulting in a resonating valence bond (RVB) superconducting state.