Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe₂

Abstract

Excitons in thin layers of semiconducting transition metal dichalcogenides are highly subject to the strongly modified Coulomb electron-hole interaction in these materials. Therefore, they do not follow the model system of a two-dimensional hydrogen atom. We investigate experimentally and theoretically excitonic properties in both the monolayer (ML) and the bilayer (BL) of MoSe2 encapsulated in hexagonal BN. The measured magnetic field evolutions of the reflectance contrast spectra of the MoSe2 ML and BL allow us to determine g-factors of intralayer A and B excitons, as well as the g-factors of the interlayer exciton. We explain the dependence of g-factors on the number of layers and excitation state can be explained using first principles calculations. Furthermore, we demonstrate that the experimentally measured ladder of excitonic s states in the ML can be reproduced using the k·p approach with the Rytova-Keldysh potential that describes the electron-hole interaction. In contrast, the analogous calculation for the BL case require taking into account the out-of-plane dielectric response of the MoSe2 BL.

Proximity-enhanced valley Zeeman splitting at the WS2/graphene interface

“…Interestingly, the exciton g-factor depends only weakly on the band gap, while the band g-factors are indeed more sensitive to E g [42], as expected from conventional III-V semiconductors within the k.p framework [41,46]. While the valley Zeeman physics in intrinsic monolayers [42][43][44][45][47][48][49] and hetero/homo-bilayers [42,45,[50][51][52][53][54][55] is relatively well understood based on the recent ab initio developments, the influence of finite carrier density [56][57][58][59][60][61][62] (see also theoretical efforts in [63,64]) or the evolution of the (in-plane) spin and orbital degrees of freedom in multilayered van der Waals heterostructures [65] still require further work.…”

Optically Addressing Exciton Spin and Pseudospin in Nanomaterials for Spintronics Applications

“…Another recent study activates the dark excitons in CrCl 3 by forming heterostructures with WSe 2 . 124 Moreover, additional studies 22−24 show that the direct or indirect nature of the electronic band gaps do change going from bulk to single layer. This can have important consequences in tuning the brightness of the excitons across different numbers of layers.…”

Highly tunable ground and excited state excitonic dipoles in multilayer 2H-MoSe2

“…Hence, in the solid-state, much emphasis has been placed on engineering interlayer excitons with large p in pioneering III-V heterostructures 11 and more recently in transition metal dichalcogenide (TMD) heterostructures [12][13][14] which host excitons with huge binding energies and thus small Bohr radii 15,16 that enable high exciton densities 17,18 . In TMD heterostructure devices, tunable interlayer excitons with large p have been realised in homobilayers [19][20][21][22][23][24][25][26][27][28][29] and heterobilayers [30][31][32][33] , even at the single exciton level [34][35][36] . However, many of the exotic collective effects underpinned by strong dipolar interactions remain to be observed, motivating further exploration of interlayer excitons and ways to manipulate their spin and optical properties.…”