Dresden 2020 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 46: Frontiers in Electronic-Structure Theory - Focus on Electron-Phonon Interactions III (joint session O/CPP/DS/HL)

HL 46.8: Talk

Wednesday, March 18, 2020, 12:30–12:45, GER 38

Ab-initio phonon self-energies and fluctuation diagnostics of phonon anomalies: lattice instabilities from Dirac pseudospin physics in transition-metal dichalcogenides — •Jan Berges¹, Erik van Loon¹, Arne Schobert¹, Malte Rösner², and Tim Wehling¹ — ¹Institute for Theoretical Physics and Bremen Center for Computational Materials Science, University of Bremen, Germany — ²Institute for Molecules and Materials, Radboud University Nijmegen, The Netherlands

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 prototypical transition-metal dichalcogenide 1H-TaS₂ reveals that coupling between the longitudinal–acoustic phonons and the electrons from an isolated low-energy metallic band is entirely responsible for phonon anomalies like mode softening and associated charge-density waves observed in this material. Our analysis allows 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-TaS₂ and similar transition-metal dichalcogenides.