Quasiparticle energy bands and Fermi surfaces of monolayer NbSe2

Abstract

A quasiparticle band structure of a single layer 2H-NbSe2 is reported by using first-principles GW calculation. We show that a self-energy correction increases the width of a partially occupied band and alters its Fermi surface shape when comparing those using conventional mean-field calculation methods. Owing to a broken inversion symmetry in the trigonal prismatic single layer structure, the spin-orbit interaction is included and its impact on the Fermi surface and quasiparticle energy bands are discussed. We also calculate the doping dependent static susceptibilities from the band structures obtained by the mean-field calculation as well as GW calculation with and without spinorbit interactions. A complete tight-binding model is constructed within the three-band third nearest neighbour hoppings and is shown to reproduce our GW quasiparticle energy bands and Fermi surface very well. Considering variations of the Fermi surface shapes depending on self-energy corrections and spin-orbit interactions, we discuss the formations of charge density wave (CDW) with different dielectric environments and their implications on recent controversial experimental results on CDW transition temperatures.

Coexistence of Elastic Modulations in the Charge Density Wave State of 2H-NbSe2

“…Full optimization of the non-modulated structure of single-layer NbSe 2 leads to a lattice constant of 3.48 Å, in good agreement with plane-wave type DFT studies, 11 3.47 Å, and the experimental value for the bulk, 3.44 Å. 8 The band structure and Fermi surface of single-layer NbSe 2 in both modulated [10][11][12] and non modulated [14][15][16] structures have been discussed before. Such Fermi surface contains rounded hexagons and rounded triangles centered at Γ and K points of the Brillouin zone (BZ), respectively.…”

QuasiparticleGWband structures and Fermi surfaces of bulk and monolayerNbS2

“…Hence, it should be sufficient to evaluate the magnitude of the spin splitting on the level of DFT and impose the same splitting on the GW results. Kim and Son [34], for example, investigated the SOC effects along these lines in the isoelectric and isostructural NbSe 2 . As we show in Appendix A, for both bulk ( Fig.…”

Dichotomy of saddle points in energy bands of a monolayer NbSe$_2$

“…For example, the indirect band gap of bulk TMDs changes to be a direct one in their monolayer 5,6 . Moreover, the Coulomb interaction as well as effects of environment such as substrates on which a single layer placed become to be essential in altering low energy physics [7][8][9][10][11][12] . Like the cases in semiconducting TMDs, the metallic ones also show several intriguing changes as their thickness decreases [13][14][15][16] .…”

“…A single layer of 2H-NbSe 2 also exhibits a similar phase diagram with a different set of critical temperatures for the states 18,19 . Since there is no apparent diverging susceptibility for the bulk and monolayer NbSe 2 12,[20][21][22][23] , the weak coupling scenario for the CDW may not work very well and several other proposals have been put forward [24][25][26][27][28] . Among those, there is an alternative weak coupling scenario of CDW formation originating from the nesting van Hove singularities (vHSs) at saddle points 29 .…”

“…The induced Rashba spin-orbit interaction can lead to nontrivial spin textures lying on the plane, which is different from the Ising-type spin orientation 38,39 of the mirror-symmetric structures. A single layer of NbSe 2 has a merit in that the energetic position of vHSs in NbSe 2 is quite close to the Fermi energy (E F ) 12 , quite contrary to the case of graphene where vHSs are very far away from E F 40,41 . Therefore, we expect interesting spin-related physical properties from interplay between spin textures and distinctive vHSs in the monolayer of NbSe 2 that can be easily accessible in experiments.…”