Two-Poton Correlations of Luminescence under Bose-Einstein Condensation of Dipolar Excitons

TL;DR

This study investigates two-photon correlations in luminescence during Bose-Einstein condensation of dipolar excitons, revealing photon bunching near the threshold and its temperature dependence, indicating a phase transition in the exciton gas.

Contribution

First measurement of two-photon correlations in dipolar exciton condensates showing photon bunching behavior near the phase transition.

Findings

Photon bunching observed near condensation threshold

Photon bunching decreases and vanishes at high excitation above threshold

Photon bunching is highly temperature-sensitive

Abstract

Correlations of luminescence intensity have been studied under Bose-Einstein condensation of dipolar excitons in the temperature range of 0.45-4.2 K. Photoexcited dipolar excitons were collected in a lateral trap in GaAs/AlGaAs Schottky-diode heterostructure with single wide (25 nm) quantum well under applied electric bias. Two-photon correlations were measured with the use of a classical Hanbury Brown - Twiss intensity interferometer (time resolution ~0.4 ns). Photon "bunching" has been observed near the Bose condensation threshold of dipolar excitons determined by the appearance of a narrow luminescence line of exciton condensate at optical pumping increase. The two-photon correlation function shows super-poissonian distribution at time scales of system coherence (<~1 ns). No photon bunching was observed at the excitation pumping appreciably below the condensation threshold. At excitation pumping increasing well above the threshold, when the narrow line of exciton condensate grows in the luminescence spectrum, the photon bunching is decreasing and finally vanishes - the two-photon correlator becomes poissonian reflecting the single-quantum-state origin of excitonic Bose condensate. Under the same conditions a first-order spatial correlator, measured by means of the luminescence interference from spatially separated condensate parts, remains significant. The discovered photon bunching is rather sensitive to temperature: it drops several times with temperature increase from 0.45 K up to 4.2 K. If assumed that the luminescence of dipolar excitons collected in the lateral trap reflects directly coherent properties of interacting exciton gas, the observed phenomenon of photon bunching nearby condensation threshold manifests phase transition in interacting exciton Bose gas.