Frequency-dependent substrate screening of excitons in atomically thin transition metal dichalcogenide semiconductors

Abstract

Atomically thin layers of transition metal dichalcogenides (TMDCs) exhibit exceptionally strong Coulomb interaction between charge carriers due to the two-dimensional carrier confinement in connection with weak dielectric screening. The van der Waals nature of interlayer coupling makes it easy to integrate TMDC layers into heterostructures with different dielectric or metallic substrates. This allows to tailor electronic and optical properties of these materials, as Coulomb interaction inside atomically thin layers is very susceptible to screening by the environment. Here we theoretically investigate dynamical screening effects in TMDCs due to bulk substrates doped with carriers over a large density range, thereby offering three-dimensional plasmons as tunable degree of freedom. We report a wide compensation of renormalization effects leading to a spectrally more stable exciton than predicted for static substrate screening, even if plasmons and excitons are in resonance. We also find a nontrivial dependence of the single-particle band gap on substrate doping density due to dynamical screening. Our investigation provides microscopic insight into the mechanisms that allow for manipulations of TMDC excitons by means of arbitrary plasmonic environments on the nanoscale. arXiv:1804.01352v1 [cond-mat.mtrl-sci]

Probing many-body interactions in monolayer transition-metal dichalcogenides

“…1-12 Their two-dimensional (2D) character and reduced screening enable the formation of tightly-bound excitons, whose response to electrostatic doping provides valuable information on the Coulomb interactions of few-particle complexes, [36][37][38][39][40] or many-body effects when excitons interact with the background charge. [41][42][43][44][45][46][47][48] The dependence of the spectral position of the neutral exciton, X 0 , on the gate-induced charge density is usually governed by two competing effects: Screening and band-gap renormalization (BGR). [49][50][51][52] The background charge screens the electron-hole interaction of photoexcited bound pairs, thereby reducing the binding energy and causing X 0 to blueshift towards the continuum of free electron-hole pairs.…”

Coulomb-Engineered Heterojunctions and Dynamical Screening in Transition Metal Dichalcogenide Monolayers

“…By embedding 2D materials in spatially inhomogeneous dielectric environments, Coulomb engineered heterostructures with spatially changing quasiparticle band gaps [8][9][10][11][12] can be created. In recent years, this approach to non-invasively manipulate 2D materials has become a promising field of research 9,[13][14][15][16][17][18][19][20][21][22][23][24] .…”

Observation of Dynamic Screening in the Excited Exciton States in Multi-layered MoS$_2$

“…The excitons are continuously annihilated and recreated through exchange interactions [15] and scattered to free-carriers [16][17][18]; therefore, the Coulomb potential that binds the excitons is not static in time. Some recent theoretical studies indicate certain "characteristic frequencies" at which exciton screening is predominant [13,19]. Nevertheless, one major bottleneck in the understanding of the dynamic nature of Coulomb screening is the severe lack of experimental evidence.…”