Fano-Resonance Gain by Dephasing Electron--Hole Cooper Pairs in Semiconductors

A genuine many-body feature in semiconductor lasers is theoretically found in the gain spectra when a BCS-type (Bardeen--Cooper--Schrieffer) electron--hole (eh) pairing instability occurs during low-temperature operation. Owing to the finite dephasing time of eh pairs, an ultranarrow Fano-resonance gain between a bound eh pair and a continuum of unbound (plasma-like) eh pairs is found close to the phase-transition point. As a result, single-mode laser operation is strongly modified relative to the conventional laser operation using the Lorentzian-type eh plasma gain. Sharp Fano-resonance gain occurs owing to the Hopf bifurcation in the poles of the optical susceptibility.