Optically Induced Symmetry Breaking Due to Nonequilibrium Steady State Formation in Charge Density Wave Material...

The strongly correlated charge density wave (CDW) phase of 1T-TiSe₂ is of interest to verify the claims of a chiral order parameter. Characterization of the symmetries of 1T-TiSe₂ 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-TiSe₂ by using the circular photogalvanic effect. We observe that the ground state of the CDW phase (D₃) is achiral. However, laser excitation above a threshold intensity transforms 1T-TiSe₂ into a nonequilibrium chiral phase (C₃), 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-TiSe₂, 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.