Common microscopic origin of the phase transitions in Ta2NiS5 and the excitonic 
insulator candidate Ta2NiSe5

Windgätter, L.; Rösner, M.; Mazza, G.; Hübener, H.; Georges, A.; Millis, A. J.; Latini, S.; Rubio, A.

doi:10.1038/s41524-021-00675-6

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Common microscopic origin of the phase transitions in Ta₂NiS₅ and the excitonic insulator candidate Ta₂NiSe₅

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Windgätter, L.
Theory Group, Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
International Max Planck Research School for Ultrafast Imaging & Structural Dynamics (IMPRS-UFAST), Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;

Hübener, H.
Theory Group, Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;

Latini, S.
Theory Group, Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;

Rubio, A.
Theory Group, Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
Center for Computational Quantum Physics, Flatiron Institute;
Nano-Bio Spectroscopy Group, Departamento de Física de Materiales, Universidad del País Vasco;

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https://arxiv.org/abs/2105.13924
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https://doi.org/10.1038/s41524-021-00675-6
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41524_2021_675_MOESM1_ESM.pdf
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Citation

Windgätter, L., Rösner, M., Mazza, G., Hübener, H., Georges, A., Millis, A. J., et al. (2021). Common microscopic origin of the phase transitions in Ta₂NiS₅ and the excitonic insulator candidate Ta₂NiSe₅. npj Computational Materials, 7(1): 210. doi:10.1038/s41524-021-00675-6.

Cite as: https://hdl.handle.net/21.11116/0000-0009-AAAC-6

Abstract

The structural phase transition in Ta2NiSe5 has been envisioned as driven by the formation of an excitonic insulating phase. However, the role of structural and electronic instabilities on crystal symmetry breaking has yet to be disentangled. Meanwhile, the phase transition in its complementary material Ta2NiS5 does not show any experimental hints of an excitonic insulating phase. We present a microscopic investigation of the electronic and phononic effects involved in the structural phase transition in Ta2NiSe5 and Ta2NiS5 using extensive first-principles calculations. In both materials the crystal symmetries are broken by phonon instabilities, which in turn lead to changes in the electronic bandstructure also observed in the experiment. A total energy landscape analysis shows no tendency towards a purely electronic instability and we find that a sizeable lattice distortion is needed to open a bandgap. We conclude that an excitonic instability is not needed to explain the phase transition in both Ta2NiSe5 and Ta2NiS5.