Optical Control of Chirality and Ferroaxial Domains

by Michael Fechner (Max Planck Institute for the Structure and Dynamics of Matter, Hamburg (Germany))

Thursday 22 Jan 2026, 10:00 → 11:00 Europe/Rome

Aula Rasetti (Dip. di Fisica - edificio G. Marconi)

Ferroic orders arise from collective quantum interactions that stabilize long-range electronic arrangements. Here, we demonstrate optical control of such orders using intense terahertz (THz) pulses. Two key cases are presented.

First, we show that linearly polarized THz pulses can induce chirality [1] in the achiral piezoelectric boron phosphate (BPO₄). Because chirality requires the simultaneous breaking of all mirror and roto-inversion symmetries, its induction in nonchiral systems is highly nontrivial. We find that resonant excitation of one of two orthogonal, degenerate vibrational modes generates a chiral order parameter, with handedness determined by the selected mode.

Second, we demonstrate switching of ferroaxial domains [2]. Unlike conventional ferroics, ferroaxial states are bistable yet preserve both inversion and time-reversal symmetry, making them robust against depolarizing fields but difficult to manipulate. By coherently driving circularly polarized THz phonon modes, we create an effective axial field that enables ultrafast domain switching. The switched domains remain stable for hours and can be reversed with pulses of opposite helicity.

Our results establish a pathway for optical control of chirality and ferroaxial order, opening opportunities for ultrafast, robust information storage.

[1] Z. Zeng, et al., Science 387, 431 (2025)

[2] Z. Zeng, et al. arXiv:2506.10682, (2025)