Exciton-Polariton Mediated Superconductivity

Abstract

We revisit the exciton mechanism of superconductivity in the framework of microcavity physics, replacing virtual excitons as a binding agent of Cooper pairs by excitations of an exciton-polariton Bose-Einstein condensate. We consider a model microcavity where a quantum well with a two dimensional electron gas is sandwiched between two undoped quantum wells, where a polariton condensate is formed. We show that the critical temperature for superconductivity dramatically increases with the condensate population, opening a new route towards high temperature superconductivity. [5,6]. Their in-plane dispersion is strongly nonparabolic. Near the ground state corresponding to zero in-plane wavevector, an extremely small polariton mass-averaging the exciton mass and the much smaller cavity-photon mass-brings the critical temperature for quantum degeneracy up to room temperature [7,8]. On the other hand, at wavevectors exceeding the wavevector of light at the exciton resonance frequency, the polariton dispersion becomes exciton-like and its effective mass exceeds that near the band minimum by four orders of magnitude (see Fig. 1). Exciton-polaritons are electrically neutral and cannot carry electric current. However, they may coexist and interact with free electrons or holes, if these carriers are introduced in the same QW with the excitons or in a neighboring QW [9]. When confined together, exciton-polaritons and free carriers form a BoseFermi mixture which is expected to exhibit peculiar optical and electronic properties. In this Letter, we study the possibility of superconductivity in semiconductor microcavities containing both undoped QWs and thin n-doped semiconductor layers. We show that exciton-polariton mediated superconductivity is possible.Conventional superconductivity occurs at low temperatures and can be described within the framework of BCS theory [10], which relies on the formation of Cooper pairs. Following the discovery of a phonon-mediated attraction between electrons [11], Cooper found that two electrons on top of a Fermi sea always form a bound state, however small the (attractive) interaction between them [12]. This instability results in the so-called BCS state (coherent state of Cooper pairs), that leads to a gap in the spectrum of excitations, responsible for superconductivity. In the currently available high-T C superconductors (the cuprates), an electron pairing is also thought to be realized through a mediating boson, although probably not the phonon [13]. Excitons have been proposed as suitable mediating bosons to achieve higher critical temperatures of superconductivity in specially designed heterostructures ([14], see [15] for a review). As compared to phonons, the characteristic cut-off energy above which the attractive character of the interaction is lost for the excitons is several orders of magnitude higher and the critical temperature is therefore expected to be sufficiently increased with respect to the BCS superconductors. One possible implementation of this idea is the socalled sandw...

An exciton-polariton mediated all-optical router

“…A set of distinctive but peculiar properties of polaritons engender a series of intriguing fundamental many-body effects and phenomena ranging from quasi-condensation [12] and superfluidity [13] to the Josephson effect [14,15] or polariton-mediated superconductivity [16]. Naturally, the utmost fascinating feature of exciton polaritonswhich represent exciton-photon mixtures -is the possibility to control, manipulate and monitor high-speed disorder-proof optical signals.…”

Cavity-Enhanced Transport of Charge

“…An emerging topic of interest is the modification of material properties using either external electro-magnetic radiation [54][55][56] or spatially confined modes such as in cavity quantum electrodynamics [57][58][59][60][61][62][63]. Recent experiments with organic semiconductors have demonstrated a dramatic enhancement of charge conductivity when molecules interact strongly with a surface plasmon mode [64].…”

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“…It is easy to show that the Cooper coupling constant scales as the occupation number of the BEC which can be directly controlled by optical pumping. This opens a perspective for the realisation of light-mediated superconductivity with very high T c [43]. The gap width and the Cooper pair size in this case would also be controlled by the intensity of pumping light, which would pave way to optical band engineering and other interesting applications.…”