Fermi edge singularity in neutral electron-hole system

TL;DR

This paper demonstrates that separating electron and hole layers in optically excited systems enables the creation of dense, ultracold electron-hole systems, revealing Fermi edge singularity indicative of excitonic Cooper pairing.

Contribution

It introduces a novel layered structure approach to achieve dense, cold e-h systems and observes Fermi edge singularity as evidence of excitonic Cooper pairing.

Findings

Enhanced photoluminescence at Fermi energy

Observation of Fermi edge singularity

Layer separation increases e-h density and lifetime

Abstract

In neutral dense electron-hole (e-h) systems at low temperatures, theory predicts Cooper-pair-like excitons at the Fermi energy and a BCS-like exciton condensation. Optical excitation allows creating e-h systems with the densities controlled by the excitation power. However, the intense optical excitations required to achieve high densities cause substantial heating of the e-h system that prevents the realization of dense and cold e-h systems in conventional semiconductors. In this work, we study e-h systems created by optical excitation in separated electron and hole layers. The layer separation increases the e-h recombination time and, in turn, the density for a given optical excitation by orders of magnitude and, as a result, enables the realization of the dense and cold e-h system. We found a strong enhancement of photoluminescence intensity at the Fermi energy of the neutral dense ultracold e-h system that evidences the emergence of excitonic Fermi edge singularity due to the Cooper-pair-like excitons at the Fermi energy.