Interlayer hybridization and moiré superlattice minibands for electrons and excitons in heterobilayers of transition-metal dichalcogenides

Abstract

Geometrical moiré patterns, generic for almost aligned bilayers of two-dimensional (2D) crystals with similar lattice structure but slightly different lattice constants, lead to zone folding and miniband formation for electronic states. Here, we show that moiré superlattice (mSL) effects in MoSe2/WS2 and MoTe2/MoSe2 heterobilayers that feature alignment of the band edges are enhanced by resonant interlayer hybridization, and anticipate similar features in twisted homobilayers of TMDs, including examples of narrow minibands close to the actual band edges. Such hybridization determines the optical activity of interlayer excitons in transition-metal dichalcogenide (TMD) heterostructures, as well as energy shifts in the exciton spectrum. We show that the resonantly hybridized exciton (hX) energy should display a sharp modulation as a function of the interlayer twist angle, accompanied by additional spectral features caused by umklapp electron-photon interactions with the mSL. We analyze the appearance of resonantly enhanced mSL features in absorption and emission of light by the interlayer exciton hybridization with both intralayer A and B excitons in MoSe2/WS2, MoTe2/MoSe2, MoSe2/MoS2, WS2/MoS2, and WSe2/MoSe2. arXiv:1809.09257v2 [cond-mat.mes-hall]

Direct observation of minibands in a twisted graphene/WS 2 bilayer

“…The minibands are absent in the case of the θ 2 -domain as the superlattice potential gets weaker at high twist angles leading to a reduced photoemission intensity. This result is both consistent with theoretical calculations [30] and photoemission results of epitaxial graphene on Ir(111)[18], and with detailed theory on the origins of minibands in TMD/TMD heterobilayers [12]. The observation of WS 2 minibands also implies the existence of mini Dirac cones replicated by the same reciprocal lattice vector in the graphene.…”

“…[18], and with detailed theory on the origins of minibands in TMD/TMD heterobilayers [12]. The observation of WS 2 minibands also implies the existence of mini Dirac cones replicated by the same reciprocal lattice vector in the graphene.…”

“…heterostructures, opening multiple new avenues for generating materials with enhanced functionality such as tunable electronic correlations [11] and tailored selection rules for optical transitions [12].…”

Hybridized intervalley moiré excitons and flat bands in twisted WSe2 bilayers

“…Within the mBZ the hybridization of bands only occurs at a fixed momentum, however the mixing can involve different moiré subbands. 32 In contrast to the K point, high-symmetry points deep within the BZ (such as Λ and Γ) only have equivalent states outside of the first BZ. Since interlayer hopping strongly decreases for large momenta, this additional mixing is negligible, 33 so that the dispersion at the Λ and Γ valley does not split into subbands.…”

Formation and tuning of moiré excitons in large-twist angle WS2/MoSe2 heterobilayers

“…However, increasing the twist angle has led to suppression of measurable features of moiré excitons. In WS 2 /MoSe 2 heterobilayers, it was suggested that the resonant interlayer hybridization amplifies the moiré superlattice effects on the electronic structure [19]; yet only a single resonance was resolved as the twist angle deviates significantly from 0 • or 60 • [18].…”