Optically Induced Symmetry Breaking Due to Nonequilibrium Steady State Formation in Charge Density Wave Material 1T-TiSe 2 .

The strongly correlated charge density wave (CDW) phase of 1T-TiSe 2 is of interest to verify the claims of a chiral order parameter. Characterization of the symmetries of 1T-TiSe 2 is critical to understand the origin of its intriguing properties. Here we use very low-power, continuous wave laser excitation to probe the symmetries of 1T-TiSe 2 by using the circular photogalvanic effect. We observe that the ground state of the CDW phase ( D 3 d ) is achiral. However, laser excitation above a threshold intensity transforms 1T-TiSe 2 into a nonequilibrium chiral phase ( C 3 ), which changes the electronic correlations in the material. The inherent sensitivity of the photogalvanic technique to structural symmetries provides evidence of the different optically driven phase of 1T-TiSe 2 , which allows us to assign symmetry groups to these states. Our work demonstrates that optically induced phase change can occur at extremely low optical intensities in strongly correlated materials, providing a pathway to engineer new phases using light.