Electrical tuning of branched flow of light.

Branched flows occur ubiquitously in various wave systems, when the propagating waves encounter weak correlated scattering potentials. Here we report the experimental realization of electrical tuning of the branched flow of light using a nematic liquid crystal (NLC) system. We create the physical realization of the weakly correlated disordered potentials of light via the inhomogeneous orientations of the NLC. We demonstrate that the branched flow of light can be switched on and off as well as tuned continuously through the electro-optical properties of NLC film. We further show that the branched flow can be manipulated by the polarization of the incident light due to the optical anisotropy of the NLC film. The nature of the branched flow of light is revealed via the unconventional intensity statistics and the rapid fidelity decay along the light propagation. Our study unveils an excellent platform for the tuning of the branched flow of light which creates a testbed for fundamental physics and offers a new way for steering light.

Topological Defect Guided Order Evolution across the Nematic-Smectic Phase Transition.

Topological defects usually emerge and vary during the phase transition of ordered systems. Their roles in thermodynamic order evolution keep being the frontier of modern condensed matter physics. Here, we study the generations of topological defects and their guidance on the order evolution during the phase transition of liquid crystals (LCs). With a given preset photopatterned alignment, two different types of topological defects are achieved depending on the thermodynamic process. Because of the memory effect of LC director field across the Nematic-Smectic (N-S) phase transition, a stable array of toric focal conic domains (TFCDs) and a frustrated one are generated in S phase, respectively. The frustrated one transfers to a metastable TFCD array with a smaller lattice constant, and further changes to a crossed-walls type N state due to the inheritance of orientational order. A free energy on temperature diagram and corresponding textures vividly describe the phase transition process and the roles of topological defects in the order evolution across the N-S phase transition. This Letter reveals the behaviors and mechanisms of topological defects on order evolution during phase transitions. It paves a way for investigating topological defect guided order evolution which is ubiquitous in soft matter and other ordered systems.