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Interatomic potential theory on the phase transition of charge density wave in transition metal dichalcogenides

Patterns and periods of charge density waves (CDW) in transition metal dichalcogenides exhibit complex phase diagrams that depend on pressure, temperature, metal intercalation, or chalcogen alloying. The phase diagrams have been understood in the context of phenomenological Landau free energy model, but the microscopic mechanisms underlying them are still not clear. Here, we present a new microscopic theory based on the interatomic potential, and have explicitly calculated temperature-dependent phase diagrams using the interatomic potential extracted from first-principles calculations. With detailed atomic structures, the calculated phase diagram of monolayer H-TaSe2 successfully reproduces the experimental features such as commensurate lock-in and stripe phase. Our work shows the complex behaviors of charge density wave are originated from the relatively simple structure of the interatomic potential and elucidates the role of lattice anharmonicity on the CDW phase transition.