  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.
