Faculté des sciences

Ab initio many-body effects in TiSe₂: A possible excitonic insulator scenario from GW band-shape renormalization

Cazzaniga, M. ; Cercellier, H. ; Holzmann, M. ; Monney, Claude ; Aebi, Philipp ; Onida, Giovanni ; Olevano, V.

In: Physical Review B - Condensed matter and materials physics, 2012, vol. 85, no. 19, p. 195111

We present both theoretical ab-initio results within the Hedin's GW approximation and experimental angle-resolved photoemission and scanning tunneling spectroscopy measurements on TiSe₂. With respect to the density-functional Kohn-Sham metallic picture, the many-body GW self-energy leads to a ≈0.2-eV band-gap insulator consistent with our STS spectra at 5 K. The highest valence and the lowest... Plus

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    Summary
    We present both theoretical ab-initio results within the Hedin's GW approximation and experimental angle-resolved photoemission and scanning tunneling spectroscopy measurements on TiSe₂. With respect to the density-functional Kohn-Sham metallic picture, the many-body GW self-energy leads to a ≈0.2-eV band-gap insulator consistent with our STS spectra at 5 K. The highest valence and the lowest conduction bands are strongly renormalized, with a loss of k² parabolic dispersion toward a k⁴ shape. In particular, GW moves the top of valence moved toward a circle of points away from Γ, arising in a Mexican hat shape commonly associated with an excitonic insulator. Our calculations are in good agreement with experiment.