# Giant ultrafast Kerr effect in type-II superconductors

## TL;DR

This paper introduces a new model demonstrating that type-II superconductors exhibit an exceptionally large Kerr effect and high-harmonic generation at low intensities, revealing their potential for nonlinear THz applications.

## Contribution

A novel theoretical model for ultrafast Kerr effect and high-harmonic generation in type-II superconductors, highlighting their unprecedented nonlinear susceptibility.

## Key findings

- Type-II superconductors have the highest nonlinear susceptibility in the THz regime.
- They exhibit high-harmonic generation at low incident intensities.
- The model explains the destruction of Cooper pairs leading to large nonlinear effects.

## Abstract

We study the ultrafast Kerr effect and high-harmonic generation in type-II superconductors by formulating a new model for a time-varying electromagnetic pulse normally incident on a thin-film superconductor. It is found that type-II superconductors exhibit exceptionally large $\chi^{(3)}$ due to the progressive destruction of Cooper pairs, and display high-harmonic generation at low incident intensities, and the highest nonlinear susceptibility of all known materials in the THz regime. Our theory opens up new avenues for accessible analytical and numerical studies of the ultrafast dynamics of superconductors.