Exploring Superconductivity under Strong Coupling with the Vacuum Electromagnetic Field

TL;DR

This study demonstrates that coupling superconductors to vacuum electromagnetic fields via surface plasmons can modify their critical temperatures without external lasers, revealing a new method to control superconductivity.

Contribution

It introduces a novel approach using strong light-matter interactions with surface plasmons to alter superconducting transition temperatures in different materials.

Findings

YBCO $T_c$ decreased from 92 K to 86 K

Rb$_3$C$_{60}$ $T_c$ increased from 30 K to 45 K

Modification achieved without external laser fields

Abstract

Light-matter interactions have generated considerable interest as a means to manipulate material properties. Light-induced superconductivity has been demonstrated using pulsed lasers. An attractive alternative possibility is to exploit strong light-matter interactions arising by coupling phonons to the vacuum electromagnetic field of a cavity mode as has been suggested and theoretically studied. Here we explore this possibility for two very different superconductors, namely YBCO (YBa$_2$Cu$_3$O$_{6+x}$) and Rb$_3$C$_{60}$, coupled to surface plasmon polaritons, using a novel cooperative effect based on the presence of a strongly coupled vibrational environment allowing efficient dressing of the otherwise weakly coupled phonon bands of these compounds. By placing the superconductor-surface plasmon system in a SQUID magnetometer, we find that the superconducting transition temperatures ($T_{c}$) for both compounds are modified in the absence of any external laser field. For YBCO, $T_{c}$ decreases from 92 K to 86 K while for Rb$_3$C$_{60}$, it increases from 30 K to 45 K at normal pressures. In the latter case, a simple theoretical framework is provided to understand these results based on an enhancement of the electron-phonon coupling. This proof-of-principle study opens a new tool box to not only modify superconducting materials but also to understand the mechanistic details of different superconductors.