# Photon Energy Dependence of Kerr Rotation in Chalcogenide Superlattices

## TL;DR

This study investigates how photon energy influences Kerr rotation in chalcogenide superlattices, revealing that nonlinear optical effects vary with photon energy and are linked to electronic transitions and interface states.

## Contribution

It demonstrates the photon energy dependence of Kerr rotation signals and links the effects to specific electronic transitions and nonlinear susceptibilities in superlattices.

## Key findings

- Kerr rotation signals increase as photon energy decreases.
- SIFE response linked to third-order nonlinear susceptibility.
- SOKE magnitude reflects cascading second-order nonlinear susceptibility.

## Abstract

We report on pump-probe based helicity dependent time-resolved Kerr measurements of chalcogenide superlattices, consisting of alternately stacked GeTe and Sb$_{2}$Te$_{3}$ layers under infrared excitation. The Kerr rotation signal consists of the specular Inverse Faraday effect (SIFE) and the specular optical Kerr effect (SOKE), both of which are found to monotonically increase with decreasing photon energy over a sub-eV energy range. Although the dependence of the SIFE can be attributed to a response function of direct third-order nonlinear susceptibility, the magnitude of the SOKE reflects cascading second-order nonlinear susceptibility resulting from electronic transitions from bulk valence band to interface-originating Dirac states of the superlattice.