Ab initio phonon self-energies and fluctuation diagnostics of phonon anomalies: Lattice instabilities from Dirac pseudospin physics in transition metal dichalcogenides
Jan Berges, Erik G. C. P. van Loon, Arne Schobert, Malte Rösner, Tim O. Wehling
备注：
Revised manuscript with ancillary scripts and data, 15 pages, 9 figures
We present an ab initio approach for the calculation of phonon self-energies and their fluctuation diagnostics, which allows us to identify the electronic processes behind phonon anomalies. Application to the transition-metal-dichalcogenide monolayer 1H-TaS$_2$ reveals that coupling between the longitudinal-acoustic phonons and the electrons from an isolated low-energy metallic band is entirely responsible for phonon anomalies such as the mode softening and associated charge-density waves observed in this material. Our analysis allows us to distinguish between different mode-softening mechanisms including matrix-element effects, Fermi-surface nesting, and Van Hove scenarios. We find that matrix-element effects originating from a peculiar type of Dirac pseudospin textures control the charge-density-wave physics in 1H-TaS$_2$ and similar transition metal dichalcogenides.
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International Research Centre Magtop, Institute of Physics, Polish Academy of Sciences（波兰科学院物理研究所磁学国际研究中心）；Institute of Physics, Polish Academy of Sciences（波兰科学院物理研究所）
