Orateur
Description
The interplay between lattice and electron degrees of freedom can give rise to complex ordered states in quantum materials. Here, we use high-resolution optical spectroscopy to investigate TiSe2, a material whose charge-ordered phase has been debated for decades. We discover a previously unobserved pronounced splitting of a doubly degenerate Eu optical phonon at the charge-density-wave transition. This directly reveals the breaking of three-fold rotational symmetry of the unit cell in a one-step transition. The results rule out the previously proposed centrosymmetric structure and points to the possibility of a low-temperature chiral charge-ordered state. Our findings demonstrate that carefully tracking optical phonons as a function of temperature provides a sensitive probe of subtle symmetry breaking. In this talk, I will recapitulate the fundamentals of charge density wave physics and discuss why we should still expect to find unconventional charge-ordered phases in nature. I will then focus on the complex charge-ordered phase of TiSe2 and show how our novel high-resolution optical spectroscopy measurements provide new insights into its underlying nature
