Steady-states and response functions of the periodically driven O(N) scalar field theory

TL;DR

This paper explores the complex phase diagram of a driven O(N) scalar field theory coupled to a thermal bath, revealing novel phases including oscillating order parameters, a Meissner polariton, and superconducting-like responses relevant to light-induced phenomena.

Contribution

It introduces the concept of a Meissner polariton and characterizes various phases of a driven scalar field theory with implications for light-induced superconductivity.

Findings

Identification of symmetry-broken phases with oscillating order parameters

Discovery of the Meissner polariton as a hybrid light-order mode

Observation of superconducting-like response near symmetry-breaking onset

Abstract

We investigate the phase diagram of a relativistic, parametrically driven O($N$)-symmetric theory coupled to a Markovian thermal bath. Our analysis reveals a rich variety of phases, including both uniform and spatially modulated symmetry-broken states, some of which feature an order parameter oscillating at half the drive frequency. When coupled to a background electromagnetic potential, these phases exhibit a Meissner effect, in the sense that the photon acquires a mass term. However, if the order parameter oscillates around a sufficiently small value, a fraction of an externally applied magnetic field can penetrate the sample in the form of a standing wave. We dub this property a \textit{Meissner polariton}, that is, a collective mode resulting from the hybridization of light with order parameter oscillations. Furthermore, near the onset of symmetry breaking, strong fluctuations give rise to a superconducting-like response even in the absence of a Meissner effect or of a Meissner polariton. Our results are relevant to experiments on light-induced orders, particularly superconductivity.