Long-range photon fluctuations enhance photon-mediated electron pairing and superconductivity

TL;DR

This paper explores how photon fluctuations in cavity-mediated interactions can significantly enhance superconductivity in two-dimensional materials, leading to higher critical temperatures than traditional BCS theory predicts.

Contribution

It demonstrates that photon fluctuations induce non-adiabatic pairing processes, substantially increasing the superconducting critical temperature beyond standard BCS predictions.

Findings

Photon fluctuations mediate non-BCS pairing processes.

Critical temperature can exceed BCS predictions by over an order of magnitude.

Incoherent photon pumping further enhances superconductivity.

Abstract

Recently, the possibility of inducing superconductivity for electrons in two dimensional materials has been proposed via cavity-mediated pairing. The cavity-mediated electron-electron interactions are long range, which has two main effects: firstly, within the standard BCS-type pairing mediated by adiabatic photons, the superconducting critical temperature depends polynomially on the coupling strength, instead of the exponential dependence characterizing the phonon-mediated pairing; secondly, as we show here, the effect of photon fluctuations is significantly enhanced. These mediate novel non-BCS-type pairing processes, via non-adiabatic photons, which are not sensitive to the electron occupation but rather to the electron dispersion and lifetime at the Fermi surface. Therefore, while the leading temperature dependence of BCS pairing comes from the smoothening of the Fermi-Dirac distribution, the temperature dependence of the fluctuation-induced pairing comes from the electron lifetime. For realistic parameters, also including cavity loss, this results into a critical temperature which can be more than one order of magnitude larger than the BCS prediction. Moreover, a finite average number photons (as can be achieved by incoherently pumping the cavity) adds to the fluctuations and leads to a further enhancement of the critical temperature.