Relaxation Oscillations and Ultrafast Emission Pulses in a Disordered Expanding Polariton Condensate

TL;DR

This paper investigates how disorder and reservoir dynamics in semiconductor microcavities lead to relaxation oscillations and ultrafast emission pulses in exciton-polariton condensates, combining experimental observations with numerical modeling.

Contribution

It reveals the role of disorder and reservoir properties in generating relaxation oscillations and ultrafast pulses in polariton condensates, supported by experimental and theoretical analysis.

Findings

Disorder causes complex burst-like emission patterns.

Reservoir decay dynamics induce relaxation oscillations.

Numerical simulations match experimental observations.

Abstract

Semiconductor microcavities are often influenced by structural imperfections, which can disturb the flow and dynamics of exciton-polariton condensates. Additionally, in exciton-polariton condensates there is a variety of dynamical scenarios and instabilities, owing to the properties of the incoherent excitonic reservoir. We investigate the dynamics of an exciton-polariton condensate which emerges in semiconductor microcavity subject to disorder, which determines its spatial and temporal behaviour. Our experimental data revealed complex burst-like time evolution under non-resonant optical pulsed excitation. The temporal patterns of the condensate emission result from the intrinsic disorder and are driven by properties of the excitonic reservoir, which decay in time much slower with respect to the polariton condensate lifetime. This feature entails a relaxation oscillation in polariton condensate formation, resulting in ultrafast emission pulses of coherent polariton field. The experimental data can be well reproduced by numerical simulations, where the condensate is coupled to the excitonic reservoir described by a set of rate equations. Theory suggests the existence of slow reservoir temporarily emptied by stimulated scattering to the condensate, generating ultrashort pulses of the condensate emission.