Spontaneous chiral ordering in titanium diselenide

Abstract

In this work, we studied the chiral charge density wave (CDW) phase in titanium diselenide (TiSe₂) with the circular photogalvanic effect (CPGE). Mechanically exfoliated bulk TiSe₂ flakes were obtained and implemented into nanoscale devices using standard fabrication techniques. Four samples' photocurrent response to a 120 meV laser was subsequently measured as a function of temperature and laser power. The onset of the CPGE at approximately 174 K confirms the emergence of chiral order below the regular CDW transition at 197 K. Furthermore, we were able to train the chirality of the system by cooling it while shining circularly polarized light. With this study, we have confirmed that TiSe₂ is a novel kind of material that spontaneously breaks inversion, all mirror, and roto-inversion symmetries and attains gyrotropic order, paving the way for future experimental work on similar condensed matter systems.