Anharmonic phonon frequency shift in MgB2

TL;DR

This study calculates the anharmonic phonon frequency shifts in MgB2 using density functional theory, revealing mode-specific shifts that align with experimental measurements and highlighting the importance of phonon scattering interactions.

Contribution

It introduces a detailed computational approach accounting for phonon mode scattering at different q-points, providing new insights into anharmonic effects in MgB2.

Findings

E2g mode at Gamma shifts by +5%

Shift at A point agrees with experiments

Smaller shift observed at M point

Abstract

We compute the anharmonic shift of the phonon frequencies in MgB2, using density functional theory. We explicitly take into account the scattering between different phonon modes at different q-points in the Brillouin zone. The shift of the E2g mode at the Gamma point is +5 % of the harmonic frequency. This result comes from the cancellation between the contributions of the four- and three-phonon scattering, respectively +10 % and -5 %. A similar shift is predicted at the A point, in agreement with inelastic X-ray scattering phonon-dispersion measurements. A smaller shift is observed at the M point.