Optical signatures of dynamical excitonic condensates

TL;DR

This paper investigates how optical spectroscopy can identify different dynamical regimes of excitonic condensates in bilayers and semiconductors, revealing characteristic spectral features and responses.

Contribution

It introduces a theoretical framework linking optical signatures to phase dynamics of excitonic condensates, including trapped and delocalized regimes, and compares minimal models to detailed predictions.

Findings

In-gap absorption line nearly independent of bias in trapped regime

Spectral feature frequency increases linearly with bias at larger voltages

Strong optical response near transition between dynamical states

Abstract

We theoretically study dynamical excitonic condensates occurring in bilayers with an imposed chemical potential difference and in photodoped semiconductors. We show that optical spectroscopy can experimentally identify phase-trapped and phase-delocalized dynamical regimes of condensation. In the weak-bias regime, the trapped dynamics of the order parameter's phase lead to an in-gap absorption line at a frequency almost independent of the bias voltage, while for larger biases, the frequency of the spectral feature increases approximately linearly with bias. In both cases there is a pronounced second harmonic response. Close to the transition between the trapped and freely oscillating states, we find a strong response upon application of a weak electric probe field and compare the results to those found in a minimal model description for the dynamics of the order parameter's phase and analyze the limitations of the latter.