Strong excitons in novel two-dimensional crystals: Silicane and germanane

Abstract

PACS 71.35.Cc-Intrinsic properties of excitons; optical absorption spectra PACS 73.22.-f-Electronic structure of nanoscale materials and related systems PACS 78.67.Wj-Optical properties of graphene Abstract-We show by first-principles calculations that, due to depressed screening and enhanced two-dimensional confinement, excitonic resonances with giant oscillator strength appear in hydrogenated Si and Ge layers, which qualitatively and quantitatively differ from those of graphane. Their large exciton binding energies and oscillator strengths make them promising for observation of novel physical effects and application in optoelectronic devices on the nanoscale.

Stark shift and electric-field-induced dissociation of excitons in monolayerMoS2andhBN/MoS2Haastrup1, Latini2, Bolotin3 et al. 2016Phys. Rev. B654491View full textAdd to dashboardCite

“…This is the so-called Mott-Wannier model which has been instrumental in the description of excitons in inorganic bulk semiconductors. A 2D version of the Mott-Wannier model has recently been shown to yield exciton binding energies in good agreement with BSE calculations and experiments for both freestanding [15,16,18,19,28] and supported [15,28,29] transition-metal dichalcogenide layers. The dissociation rate of the exciton is then obtained by complex scaling, which is a formally exact technique to compute resonance energies and lifetimes.…”

“…One of the hallmarks of the 2D semiconductors is the presence of strongly bound excitons with binding energies reaching up to 30% of the band gap. These large binding energies are mainly a result of the reduced dielectric screening in two dimensions [15][16][17][18][19]. Although such strongly bound excitons are highly interesting from a fundamental point of view (for example, in the context of Bose-Einstein condensates [20]) they are problematic for many of the envisioned applications of 2D materials, such as photodetectors and solar cells which rely on efficient conversion of photons into electrical currents.…”

“…For later use we note that both of these functions are analytic on the entire complex plane away from z = 0. The expression (3) for the screened interaction relies on a first-order expansion of 2D (q) around q = 0; the validity of this approximation has been demonstrated for a number of freestanding 2D semiconductors [16,18,19] and recently for MoS 2 embedded in a few layers of hBN [15]. As a rule of thumb, the linear screening approximation [Eq.…”

Theory of neutral and charged excitons in monolayer transition metal dichalcogenides

“…Such a variational solution to the 2D Hamiltonian (1) has recently been employed in related, strongly interacting 2D materials. 40,41 Our preliminary results using a numerically exact grid-based diagonalization of the Hamiltonian (1) suggest the the variational approximation is an excellent one, as will be analyzed in more detail in future work.…”

Excitons in van der Waals heterostructures: The important role of dielectric screening

“…In fact, for 2D systems the dielectric function is strongly q dependent, and a more * Corresponding author: simola@fysik.dtu.dk elaborate treatment of the screening is required [14][15][16]. This issue has been treated by several authors [14,15,17,18], who envisioned the 2D material as a strict 2D system, i.e., mathematically 2D, with a dielectric function of the form 2D (q) = 1 + 2παq,…”