Continuous Space-Time Crystal State Driven by Nonreciprocal Optical Forces

TL;DR

This paper explains the emergence of continuous space-time crystal states in plasmonic nanowire arrays as a nonreciprocal phase transition driven by radiation pressure forces, without requiring oscillator nonlinearity.

Contribution

It introduces a novel mechanism for continuous time crystal formation via nonreciprocal forces, distinct from traditional nonlinear synchronization models.

Findings

Space-time crystal state arises from nonreciprocal radiation pressure forces.

Synchronization occurs above a certain light intensity threshold.

The mechanism does not depend on oscillator nonlinearity.

Abstract

Continuous time crystals (CTCs) - media with broken continuous time translation symmetry - are an eagerly sought state of matter that spontaneously transition from a time-independent state to one of periodic motion in response to a small perturbation. The state has been realized recently in an array of nanowires decorated with plasmonic metamolecules illuminated with light. Here we show that this as-yet-unexplained CTC state can be understood as arising from a nonreciprocal phase transition induced by nonconservative radiation pressure forces among plasmonic metamolecules: above a certain intensity threshold, light drives the inhomogeneously broadened array of thermally-driven noisy nanowire oscillators to a synchronized coherent space-time crystal state and ergodicity of the system is broken. At the onset of synchronization, this mechanism does not require nonlinearity in the oscillators but depends instead on nonreciprocal forces. As such it is fundamentally different from the regimes of synchronization that depend on nonlinearity.