# Dark Solitons in Waveguide Polariton Fluids Shed Light on Interaction Constants

## TL;DR

This study investigates dark solitons in high-momentum exciton-polariton fluids, revealing how their properties depend on density and identifying a reservoir-driven nonlinearity with implications for optical fluid dynamics.

## Contribution

It provides the first analysis of dark solitons in high-momentum polariton fluids and quantifies interaction constants, highlighting reservoir effects on nonlinearity.

## Key findings

- Dark solitons form in high-momentum polariton fluids.
- Interaction constants are an order of magnitude larger with continuous waves.
- Interaction strength builds up over 100 ps due to a self-generated excitonic reservoir.

## Abstract

We study exciton-polariton nonlinear optical fluids in a high momentum regime for the first time. Defects in the fluid develop into dark solitons whose healing length decreases with increasing density. We deduce interaction constants for continuous wave polaritons an order of magnitude larger than with picosecond pulses. Time dependent measurements show a 100ps time for the buildup of the interaction strength suggesting a self-generated excitonic reservoir as the source of the extra nonlinearity. The experimental results agree well with a model of coupled photons, excitons and the reservoir.