Universal Phase Transitions of Matter in Optically Driven Cavities

Optical cavities have been widely applied to manipulate the properties of solid state materials inside them. We propose that in systems embedded within optical cavities driven by incident pump light, the pump induces generic phase transitions into new nonequilibrium steady states. This effect arises from the ponderomotive potential, the effective static potential exerted by the pump on the low energy degrees of freedom, which exhibits a universal steplike structure that pushes the matter degrees of freedom in the direction that redshifts the cavity photon modes. For a two dimensional electron liquid in a driven cavity, this steplike potential pushes the electron density to jump to a smaller value so that a hybrid cavity photon mode is redshifted to slightly below the pump frequency. Similarly, for a dirty superconductor in such a driven cavity, this potential acts on the superconducting order parameter and causes a first order phase transition to a new steady state with a smaller gap. By realistic electromagnetic modeling of the cavity that includes all cavity modes, we construct the nonequilibrium phase diagrams for experimentally relevant devices.