Abstract:
Egor will show how crystalline inversion symmetry can be dynamically broken by driving optical phonons with generic, hardening Kerr-like nonlinearities. The symmetry-broken state is reached through a parametric instability that can be accessed by driving close to half the phonon frequency. The system then settles into a steady state with inversion-symmetry-breaking phonon trajectories and strong second-harmonic generation. The time-averaged atomic positions are displaced from equilibrium, resulting in a ferroelectric rectification of the driving signal. For circularly polarized phonons, complex Lissajous-like trajectories can emerge, generating spatially structured magnetic fields within the unit cell.
More broadly, he will discuss how concepts from nonlinear dynamics, such as pattern formation and chaotic diffusion, can be exploited to control strongly driven collective modes in solids.
