Valley-spin phenomena in the moire pattern of van der Waals heterostructures*

In semiconducting transition metal dichalcogenides monolayers, the band edge carriers are described by massive Dirac cones, located at K and -K corners (valleys) of the Brillouin zone. These massive Dirac Fermions have interesting properties dependent on their valley index, which enable versatile control of the valley pseudospin. Van der Waals stacking of the 2D semiconductors into vertical heterostructures is a powerful approach towards designer quantum materials that can extend the exotic properties of the building blocks. A generic aspect of these vdW heterostructures is the formation of moiré pattern (i.e. periodic variation of local atomic registries) due to the inevitable lattice mismatch. We show that, because of the valley degeneracy of band edges in the monolayer building blocks, the moiré pattern leads to lateral modulations in the electronic, optical, and topological properties in the vdW heterostructure [1,2]. These modulations can endow heterobilayers a number of intriguing properties, including: (i) electrically switchable and strain tunable lateral superstructures of topological insulators [1]; (ii) programmable arrays of single photon emitters and entangled photon sources; and (iii) spin-orbit coupled excitonic superlattices [2].

[1] Q. Tong, H. Yu, Q. Zhu, Y. Wang, X. Xu and W. Yao, Topological Mosaic in Moiré superlattices of van der Waals heterobilayers, Nature Physics 13, 356 (2017).
[2] H. Yu, G.-B. Liu, J. Tang, X. Xu, W. Yao, Moiré excitons: From programmable quantum emitter arrays to spin-orbit–coupled artificial lattices. Science Advances 3, e1701696 (2017).