Exciton pairs coupled via the long-living phonons and their superfluorescent markers

TL;DR

This paper models the formation of exciton pairs coupled via long-living phonons in bulk materials, revealing their superfluorescent emission and providing theoretical insights aligned with experimental observations in hybrid perovskites.

Contribution

It introduces a novel theoretical framework for exciton pair formation through exciton-phonon entanglement, using multiconfiguration Hartree method on the Frohlich Hamiltonian.

Findings

Exciton pairs form via entanglement with long-living phonons.

The theory predicts superfluorescent spectra matching experiments.

Stationary solutions describe excitonic polarons and pairs.

Abstract

A system of several Wannier-Mott excitons interacting with phonons in a bulk material is considered. We show that strong exciton-phonon coupling causes the formation of a coherent two-exciton state -- the exciton pair. Unlike the biexcitons, where the photons play the role of force carrier, the exciton pair is formed via entanglement with the long-living phonon mode: (i) The essentially multi-particle theory requires excitons (cobosons composed of an electron and a hole) to satisfy the mixed Bose-Fermi statistics; (ii) This allows us to formulate a system of non-linear dynamic equations, using the multiconfiguration Hartree method applied to the Frohlich Hamiltonian. The system of equations possesses a stationary solution, which, for the case of a single exciton, describes the excitonic polaron and corresponds to the exciton pair in the two-exciton case. We also compare the fluorescent spectra of exciton polarons and exciton pairs estimated from our theory with those observed in experiments on room-temperature superfluorescence (collective emission of fluorescent light) in hybrid perovskites to give an additional insight into the superfluorescence phenomenon.