Holes in the valence band of superconducting boron-doped diamond film studied by soft X-ray absorption and emission spectroscopy

TL;DR

This study investigates the electronic structure of boron-doped diamond films, revealing the presence of hole states in the valence band that are linked to superconductivity, challenging simple models and supported by experimental and theoretical analysis.

Contribution

It provides new insights into the electronic states responsible for superconductivity in boron-doped diamond, highlighting the role of valence band holes beyond impurity states.

Findings

Large density of hole states in the valence band of superconducting samples

Hole states located about 1.3 eV below the valence band maximum

Superconductivity attributed to holes in the valence band

Abstract

Carbon- and boron-2$p$ states of superconducting and non-superconducting boron-doped diamond samples are measured using soft X-ray emission and absorption spectroscopy. For the superconducting sample, a large density of hole states is observed in the valence band in addition to the states in the impurity band. The hole states in the valence band is located at about 1.3 eV below the valence band maximum regardless of the doping level, which cannot be interpreted within a simple rigid band model. Present experimental results, combined with the first principles calculations, suggest that superconductivity is to be attributed to the holes in the valence band.