# Ultrafast Hot Phonon Dynamics in MgB$_2$ Driven by Anisotropic Electron-Phonon Coupling

## TL;DR

This paper uses first-principles calculations to show that ultrafast laser pulses induce a hot-phonon regime in MgB$_2$, significantly affecting the $E_{2g}$ phonon modes through anisotropic electron-phonon interactions.

## Contribution

It reveals the ultrafast hot-phonon dynamics in MgB$_2$ driven by anisotropic electron-phonon coupling, highlighting nonadiabatic effects in optical responses.

## Key findings

- Hot-phonon regime triggered by ultrafast laser in MgB$_2$
- Spectral signatures in ultrafast Raman spectroscopy
- Nonadiabatic processes significantly influence $E_{2g}$ mode features

## Abstract

The zone-center $E_{2g}$ modes play a crucial role in MgB$_2$, controlling the scattering mechanisms in the normal state as well the superconducting pairing. Here, we demonstrate via first-principles quantum-field theory calculations that, due to the anisotropic electron-phonon interaction, a $hot$-$phonon$ regime where the $E_{2g}$ phonons can achieve significantly larger effective populations than other modes, is triggered in MgB$_2$ by the interaction with an ultra-short laser pulse. Spectral signatures of this scenario in ultrafast pump-probe Raman spectroscopy are discussed in detail, revealing also a fundamental role of nonadiabatic processes in the optical features of the $E_{2g}$ mode.