Phonon Softening in Superconducting Diamond

TL;DR

This study observes phonon softening in boron-doped diamond near the zone center, supporting phonon-mediated superconductivity with an electron-phonon coupling parameter of about 0.33.

Contribution

It provides experimental evidence of phonon softening in superconducting diamond, confirming theoretical models of phonon-mediated pairing mechanisms.

Findings

Strong phonon softening observed near zone center

Softening increases approaching the zone center

Electron-phonon coupling parameter estimated as ~0.33

Abstract

We observe strong softening of optical phonon modes in superconducting (Tc = 4.2 K) boron doped diamond near the Brillouin zone center using inelastic x-ray scattering from a CVD-grown highly oriented sample. The magnitude of the softening, and our observation that it becomes stronger approaching zone center, supports theoretical models suggesting a phonon-mediated pairing mechanism via coupling of optical phonon modes to Fermi surfaces around the zone center. The electron-phonon coupling parameter is determined as approximately lambda= 0.33.