For TMD bilayers with small twist angles, in particular, canonical moiré superlattices are known to transform into periodic domains of distinct atomic registries in triangular or hexagonal tiling 27, 28, 29, 30, 31, 32, 33, as dictated by the competition between the intralayer strain and interlayer adhesion energies 34, 35, 36. The diversity of models invoked to explain the plethora of experimental signatures is not inherent to the theory of moiré excitons 24, 25, 26 but is instead related to variations in actual samples. The experimental results for the peak energies of the interlayer exciton photoluminescence (PL) 21, 22, g-factor 11, 22 and degree of polarization 11, 12 are inconsistent, and the PL spectra can differ substantially from spot to spot even in the same sample 23. 19), a consolidated picture of the rich experimental features remains elusive 20. Moiré effects also result in rich optical signatures of intralayer 10 and interlayer 11, 12, 13, 14 excitons that are formed by Coulomb attractions among layer-locked and -separated electrons and holes, with angle-controlled exciton valley coherence and dynamics 15, 16, optical nonlinearities 17 or correlated excitonic insulating states 18.ĭespite the extensive optical studies of moiré effects in TMD heterobilayers such as MoSe 2–WSe 2 (ref.
Periodic moiré interference patterns have profound effects on the electronic band structure due to formation of flat mini-bands that enhance many-body correlations, and induce emergent magnetism 6, correlated insulating states 2, 3, 4, 7, 8, 9 or Wigner crystals 7. Vertical assemblies of twisted or lattice-mismatched heterobilayers of two-dimensionaltransition metal dichalcogenides (TMDs) with moiré-modulated interlayer coupling give rise to correlated Hubbard-model physics 1-exhibiting signatures of collective phases in both transport 2, 3, 4, 5 and optical experiments 6, 7, 8, 9. Generalized to stacks of other two-dimensional materials, this notion of mesoscale domain formation with emergent topological defects and percolation networks will instructively expand the understanding of fundamental electronic, optical and magnetic properties of van der Waals heterostructures. Our results provide a unified perspective on moiré excitons in near-commensurate semiconductor heterostructures with small twist angles by identifying domains with exciton properties of distinct effective dimensionality, and establish mesoscopic reconstruction as a compelling feature of real samples and devices with inherent finite size effects and disorder. Here we expand the notion of such nanoscale lattice reconstruction to the mesoscopic scale of laterally extended samples and demonstrate rich consequences in optical studies of excitons in MoSe 2–WSe 2 heterostructures with parallel and antiparallel alignments. Due to finite elasticity, however, the superlattices can transform from moiré-type to periodically reconstructed patterns. Moiré effects in vertical stacks of two-dimensional crystals give rise to new quantum materials with rich transport and optical phenomena that originate from modulations of atomic registries within moiré supercells.
0 kommentar(er)
