# Real-time Observation of Phonon-Mediated $\sigma$-$\pi$ Interband Scattering in MgB2

## TL;DR

This study demonstrates how femtosecond laser pulses can selectively excite phonons in MgB2, enabling transient control of electronic carriers and revealing details of interband scattering mechanisms through optical measurements and modeling.

## Contribution

It provides the first real-time observation of phonon-mediated interband scattering in MgB2 using ultrafast spectroscopy.

## Key findings

- Selective enhancement of E2g phonons in MgB2 by femtosecond laser pulses
- Transient modulation of carrier populations in the sigma electronic subsystem
- Theoretical modeling elucidates the sigma-pi interband scattering process

## Abstract

In systems having an anisotropic electronic structure, such as the layered materials graphite, graphene and cuprates, impulsive light excitation can coherently stimulate specific bosonic modes, with exotic consequences for the emergent electronic properties. Here we show that the population of E$_{2g}$ phonons in the multiband superconductor MgB$_2$ can be selectively enhanced by femtosecond laser pulses, leading to a transient control of the number of carriers in the {\sigma}-electronic subsystem. The nonequilibrium evolution of the material optical constants is followed in the spectral region sensitive to both the a- and c-axis plasma frequencies and modeled theoretically, revealing the details of the $\sigma$-$\pi$ interband scattering mechanism in MgB$_2$.