Effect of polariton-polariton interactions on the excitation spectrum of a non-equilibrium condensate in a periodic potential

TL;DR

This study explores how polariton-polariton interactions influence the excitation spectrum of non-equilibrium condensates in periodic potentials, revealing screening effects and differences between resonant and non-resonant pumping.

Contribution

It provides experimental and theoretical insights into the screening of acoustic potentials by polariton condensates and compares resonant and non-resonant excitation effects.

Findings

Resonant pumping reduces the energy gap via screening.

Non-resonant pumping leads to coexisting condensates with different properties.

Screening effects are less pronounced in non-resonant excitation.

Abstract

Polariton condensates are investigated in periodical potentials created by surface acoustic waves using both resonant and non-resonant optical excitation. Under resonant pumping condensates are formed due to polariton parametric scattering from the pump. In this case the single particle dispersion in the presence of the condensate shows a strong reduction of the energy gap arising from the acoustic modulation, indicating efficient screening of the surface acoustic wave potential by spatial modulation of the polariton density. The observed results are in good agreement with a model based on generalised Gross-Pitaveskii equations with account taken of the spatial dependence of the exciton energy landscape. In the case of incoherent, non-resonant pumping coexisting non-equilibrium condensates with s- and p- type wavefunctions are observed, which have different energies, symmetry and spatial coherence. The energy splitting between these condensate states is also reduced with respect to the gap of the one particle spectrum below threshold, but the screening effect is less pronounced than in the case of resonantly pumped system due to weaker modulation of the pump state.