Theoretical Study of Pseudo Two‐Step Phase Transition Behaviors in Bilayer 1T‐TiSe₂

High‐temperature metal phase of bilayer and bulk 1T‐TiSe 2 will undergo two‐stage phase transition (PT) while monolayer samples undergo only one‐stage PT upon cooling. Such a surprising two‐stage PT behavior of bilayer samples has not well been understood up to now. In this study, the theoretical calculations with density functional theory revealed that so called two‐stage PT is actually a traditional one‐stage PT. One layer of bilayer 1T‐TiSe 2 will undergo a 2 × 2 × 1 charge density wave (CDW) alone, and then the 2 × 2 × 1 CDW supercells of another layer subsequently take place upon further decreasing temperature. Since the potential barriers of PT between any two CDW configurations are on the order of only several meV/TiSe 2 , it is easy to realize their transformations between various CDW configurations for bilayer 1T–TiSe 2 . In fact, the hidden order with CDW phase only in one layer or phase separation is widely present in 1T–TiSe 2 multilayer samples.