Role of surface-bound hole states in electric-field-driven superconductivity at the (110)-surface of diamond

Kazuhiro Sano; Takahiro Hattori; Kohji Nakamura

doi:10.1103/PhysRevB.96.155144

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Role of surface-bound hole states in electric-field-driven superconductivity at the (110)-surface of diamond

Kazuhiro Sano, Takahiro Hattori, Kohji Nakamura

DOI 10.1103/PhysRevB.96.155144 · Physical Review B

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Abstract

Hole states in electric-field-driven superconductivity at the (110)-surface of diamond are examined by means of first-principles calculations and one-dimensional tight-binding model calculations. It is found that surface-bound hole states confined near the surface by application of an electric field E play a key role in superconductivity. Indeed, there is a critical external electric field |Ec| (≃0.4 V/Å) for observing the superconductivity, which can be attributed to the second surface-bound hole state. With McMillan's formula and calculated phonon-electron coupling constants, we demonstrate that, in electric fields <|Ec| which correspond to a surface carrier density of ∼2.3×1013cm−2, superconductivity may not be practically observed while the superconductivity transition temperature suddenly increases at |Ec|.