Dresden 2020 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 59: Correlated Electrons: Quantum Impurities and Kondo Physics; Other Materials

TT 59.10: Vortrag

Donnerstag, 19. März 2020, 17:30–17:45, HSZ 03

Ab-initio study of the possible excitonic insulator Ta2NiSe5. Investigating the electronic properties of the structural transition and its excitonic features — •Lukas Windgaetter1, Simone Latini1, Hannes Huebener1, and Angel Rubio1,21Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany — 2Center for Computational Quantum Physics (CCQ), Flatiron Institute, 162 Fifth Avenue, New York NY 10010, USA

The excitonic insulator is a theoretically predicted phase in which a condensate of bound electron hole pairs is the electronic groundstate of the crystal. Recently Ta2NiSe5 has been proposed as a promising candidate material with many experiments hinting towards the existence of such an excitonic insulating phase. However, it is still under debate whether the high temperature phase is semi-metallic or a small gap semiconductor and how the pure structural transition which accompanies the excitonic transition affects the materials properties. To settle these questions a thorough theoretical study using ab-initio methods is needed. We present DFT and GW calculations for the high-temperature orthorhombic phase as well as for the low temperature monoclinic phase of Ta2NiSe5. We show that our results suggest, that the high temperature phase starts from a semi-metallic groundstate which becomes a semiconductor in the low temperature phase after undergoing the structural phase transition. Furthermore we investigate the phonon spectrum and identify a soft phonon mode in the high temperature phase which drives the structural transition.

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