Electric field exfoliation and high-TC superconductivity in field-effect hole-doped hydrogenated diamond (111)

We investigate the possible occurrence of field-effect induced superconductivity in the hydrogenated (111) diamond surface by first-principles calculations. By computing the band alignment between bulk diamond and the hydrogenated surface, we show that the electric field exfoliates the sample, separating the electronic states at the valence band top from the bulk projected ones. At the hole doping values considered here, ranging from n = 2.84 × 10¹³ cm⁻² to n = 6 × 10¹⁴ cm⁻², the valence band top is composed of up to three electronic bands hosting holes with different effective masses. These bands resemble those of the undoped surface, but they are heavily modified by the electric field and differ substantially from a rigid doping picture. We calculate superconducting properties by including the effects of charging of the slab and of the electric field on the structural properties, electronic structure, phonon dispersion and electron-phonon coupling. We find that at a doping level as large as n = 6 × 10¹⁴ cm⁻², the electron-phonon interaction is λ = 0.81 and superconductivity emerges with T_C ≈ 29–36 K. Superconductivity is mostly supported by in-plane diamond phonon vibrations and to a lesser extent by some out-of-plane vibrations. The relevant electron-phonon scattering processes involve both intra and interband scattering so that superconductivity is multiband in nature.