Scientific Results

Excitons bound by photon exchange

Year: 2020

Authors: Cortese E., Tran NL., Manceau JM., Bousseksou A., Carusotto I., Biasiol G., Colombelli R., De Liberato S.

Autors Affiliation: ‎Univ Southampton, Sch Phys & Astron, Southampton, Hants, England; Univ Paris Saclay, UMR 9001, CNRS, Ctr Nanosci & Nanotechnol C2N, Palaiseau, France;‎ Univ Trento, INO CNR BEC Ctr, Povo, Italy; Univ Trento, Dipartimento Fis, Povo, Italy; CNR IOM, Lab TASC, Trieste, Italy

Abstract: Electrons and holes in doped quantum wells cannot form bound states from usual Coulomb interaction. However, when the system is embedded in a cavity, the exchange of photons provides an effective attraction, leading to the creation of bound excitons.
In contrast to interband excitons in undoped quantum wells, doped quantum wells do not display sharp resonances due to excitonic bound states. The effective Coulomb interaction between electrons and holes in these systems typically leads to only a depolarization shift of the single-electron intersubband transitions(1). Non-perturbative light-matter interaction in solid-state devices has been investigated as a pathway to tuning optoelectronic properties of materials(2,3). A recent theoretical work(4)predicted that when the doped quantum wells are embedded in a photonic cavity, emission-reabsorption processes of cavity photons can generate an effective attractive interaction that binds electrons and holes together, leading to the creation of an intraband bound exciton. Here, we spectroscopically observe such a bound state as a discrete resonance that appears below the ionization threshold only when the coupling between light and matter is increased above a critical value. Our result demonstrates that two charged particles can be bound by the exchange of transverse photons. Light-matter coupling can thus be used as a tool in quantum material engineering, tuning electronic properties of semiconductor heterostructures beyond those permitted by mere crystal structures, with direct applications to mid-infrared optoelectronics.

Journal/Review: NATURE PHYSICS

Volume: 2020      Pages from: eaAUG 2020-1  to: eaAUG 2020-6

DOI: 10.1038/s41567-020-0994-6

Citations: 1
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