Effects of confinement and environment on the electronic structure and exciton binding energy of MoS2from first principles

Origin of Indirect Optical Transitions in Few-Layer MoS2, WS2, and WSe2

“…This behavior was predicted by calculations 7,[16][17][18][20][21][22] and confirmed in early photoemission experiments on WS 2 monolayer grown by van der Waals epitaxy 23 . Similarly, the conduction band valley at the Λ point (midpoint between K and Γ) shifts downward in the presence of interlayer interaction as indicated by calculations 7,16,17,[20][21][22] . In contrast, the states near the K point are comparatively less susceptible to the number of layers 4,7,9,10 .…”

“…These results suggest that excited electrons will relax to the valence band via K→Γ indirect transition for MoS 2 and WSe 2 whereas Λ→Γ transition is favored for WS 2 (dashed arrows in Figure 1). In real systems, however, excitonic and polaronic effects are expected to play a major role, leading to deviations in the relaxation pathways predicted by the static ground state picture 11,18,21,22,26 . Thus, DFT results may not be directly correlated with experimental observations.…”

“…In few-layer MX 2 , the conduction band valleys of the K and Λ points compete in energy. For bilayer MoS 2 and WS 2 , some calculations 16,17,21,22,24 show that the CBM is located at the K point while others 7,16,17,20 show that it is at the Λ point. The discrepancy is partly due to the fact that some calculations neglect spin-orbit interactions.…”

Quasiparticle self-consistentGWcalculations of the electronic band structure of bulk and monolayerV2O5

“…It has been found, in previous work on transition metal dichalcogenides, that much stronger effects result from the 2D character in GW calculations because of the important changes in 2D screening and the long-range effects in GW . 29 Reduced screening effects were already manifested in monolayer V 2 O 5 to have an effect on the phonons. 23 Here we present quasiparticle self-consistent (QS) GW calculations 30 of the pure and undoped V 2 O 5 band structure to test how well this method describes a strongly correlated 2D material.…”

High-temperature superfluidity of the two-component Bose gas in a transition metal dichalcogenide bilayer

“…The properties of direct excitons in mono-and few-layer TMDCs on a SiO 2 substrate were experimentally and theoretically investigated, identifying and characterizing not only the ground-state exciton but the full sequence of excited (Rydberg) exciton states [46]. The exciton binding energy for monolayer, few-layer and bulk TMDCs and optical gaps were evaluated using the tight-binding approximation [47], by solving the BSE [48,49], applying an effective mass model, density functional theory and subsequent random phase approximation calculations [50], and by a generalized time-dependent density-matrix functional theory approach [51]. Significant spin-orbit splitting in the valence band leads to the formation of two distinct types of excitons in TMDC layers, labeled A and B [50].…”