A new microscopic theory on charge density wave phases in transition metal dichalcogenides*

Patterns and periods of charge density waves (CDW) in transition metal dichalcogenides have rich phase diagrams depending pressure, temperature, metal intercalation, or chalcogen alloying. The phase diagrams have been explained by phenomenological Landau free energy models pioneered by McMillan, Nakanishi and Shiba. In this talk, I will present a new microscopic theory for the phase diagrams by devising the suitable interatomic potentials. From first-principles calculation, we can extract the desired interatomic potentials to construct the lattice distortion energy in a reciprocal space from which temperature-dependent phase diagrams including lattice-incommensurate structures can be explicitly obtained. We successfully reproduce the experimental phase diagrams displaying commensurate lock-in, stripe phase, and atomic structure of incommensurate charge density wave, if name a few. Our microscopic theory provides us with straightforward interpretations of several CDW phases and deepens our understanding of the phase transitions between them.