Quasidegenerate charge-density wave states in 1T-TiSe2

Transition metal dichalcogenides have been actively studied for their intriguing charge density wave (CDW) formations and their impacts on material properties. Among these, 1T-TiSe2 is well-known to exhibit a 2X2X2 CDW state transition at 200 K, but its true ground state nature remains under debate.In this study, we investigate possible CDW states in 1T-TiSe2 and their consequences for transport properties by employing first-principles electronic structure calculations and angle-resolved photoemission spectroscopy. We identify seven distinct types of 2X2X2 CDW phases, most of which have not been reported previously. All of these phases are nearly degenerate in energy with each other (< 1.41 meV per formula unit). Using the band unfolding technique, we compare the electronic band structures of these CDW phases with experimental angle-resolved photoemission spectroscopy data. Our findings support the presence of a possible second phase transition at 165 K and suggest a new intermediate CDW order between 165 and 200 K that was previously unexplored. This result provides a possible resolution to the conflict between previous reports on the ground state symmetry of 1T-TiSe2, and opens a viable route to phase engineering of 1T-TiSe2 for functional applications.