Light-induced thermomechanical reorientation and helicity flipping in ferroelectric nematic phase

The recently discovered ferroelectric nematic liquid crystals provide strong linear coupling between the ferroelectric polarization (polar director) direction and electric field. Here we show that director rotation and related domain wall motion induced by laser light absorption is observable in the ferroelectric nematic (NF) phase of the archetypal liquid crystal DIO. The observed phenomena strongly depend on the alignment of the ferroelectric polarization on the boundary plates with respect to each other and the direction of the laser light. It is found that laser absorption in the electrodes of the cell plays an essential role in the observed phenomena. The main characteristics of the findings can be explained by a torque acting on the polar director due to a temperature gradient. These experiments provide the demonstration of a thermomechanical effect that is a property of polar fluids and does not exist in the conventional paraelectric nematic and antiferroelectric phases. Ferroelectric nematic crystals exhibit strong linear coupling between the ferroelectric polarization direction and an applied electric field. Here, in the ferroelectric nematic phase of the DIO liquid crystal, director rotation and domain wall motion are induced and observed.