Fermi edge singularity in neutral electron–hole system

In neutral dense electron–hole systems at low temperatures, theory predicted Cooper-pair-like excitons exist the Fermi energy and form a Bardeen–Cooper–Schrieffer-like condensate. Optical excitations create with density controlled via excitation power. However, intense optical required to achieve high densities cause substantial heating that prevents realization of simultaneously cold in conventional semiconductors. Here we show separation electron hole layers enables system. We find strong enhancement photoluminescence intensity ultracold system demonstrates emergence an excitonic edge singularity due formation energy. Our measurements also crossover from hydrogen-like increasing density, consistent theoretical prediction smooth transition. The by is hindered caused particle recombination. Now, have been observed heterostructures separated layers.