Dynamical symmetry breaking with phonons and magnons

I show how crystalline inversion symmetry can be dynamically broken by optical phonons with generic, hardening Kerr-like non-linearities. The symmetry-broken state is reached through a parametric instability that can be accessed by driving close to half the phonon resonance. After the onset of the instability, the system settles to a steady state with inversion-symmetry breaking phonon trajectories and strong second harmonic generation. The time averaged positions of the atoms are displaced relative to equilibrium, resulting in a ferroelectric rectification of the driving signal.

If time allows, I will also outline how difficult to access antiferromagnetic resonances in the THz range can be parametrically excited with amplitude modulated signals at optical frequencies via a mechanism that I call Modulated Floquet Parametric Driving (MFPD). I will demonstrate that MFPD induces transitions to symmetry breaking steady-states in which dynamical spin patterns are formed by resonant magnon pairs.