Electronic structure of single layer 1T-NbSe2: interplay of lattice distortions, non-local exchange, and Mott–Hubbard correlations. (23rd July 2018)

• Record Type: Journal Article
• Authors: Kamil, E; Berges, J; Schönhoff, G; Rösner, M; Schüler, M; Sangiovanni, G; Wehling, T O
• Is Part Of: Journal of physics. Volume 30:Number 32(2018)
• Publication Date: 2018-07-23
• Subjects: TMDC -- Mott insulator -- charge-transfer insulator -- charge-density wave -- Star of David; Condensed matter -- Periodicals; Matière condensée -- Périodiques; Vaste stoffen; Vloeistoffen; Natuurkunde; Electronic journals; Computer network resources; 530.4105
• DOI: 10.1088/1361-648X/aad215
• Languages: English
• ISSNs: 0953-8984

Abstract

Abstract: Using ab initio calculations we reveal the nature of the insulating phase recently found experimentally in monolayer 1T-NbSe2 . We find soft phonon modes in a large part of the Brillouin zone indicating the strong-coupling nature of a charge-density-wave instability. Structural relaxation of a supercell reveals a Star-of-David reconstruction with an energy gain of 60 meV per primitive unit cell. The band structure of the distorted phase exhibits a half-filled flat band which is associated with orbitals that are delocalized over several atoms in each Star of David. By including many-body corrections through a combined GW, hybrid-functional, and DMFT treatment, we find the flat band to split into narrow Hubbard bands. The lowest energy excitation across the gap turns out to be between itinerant Se- p states and the upper Hubbard band, determining the system to be a charge-transfer insulator. Combined hybrid-functional and GW calculations show that long-range interactions shift the Se- p states to lower energies. Thus, a delicate interplay of local and long-range correlations determines the gap nature and its size in this distorted phase of the monolayer 1T-NbSe2 .