Heterostructures composed of two-dimensional van der Waals(vdW)materials allow highly controllable stacking,where interlayer twist angles introduce a continuous degree of freedom to alter the electronic band structures and excitonic physics.Motivated by the discovery of Mott insulating states and superconductivity in magic-angle bilayer graphene,the emerging research fields of“twistronics”and moiréphysics have aroused great academic interests in the engineering of optoelectronic properties and the exploration of new quantum phenomena,in which moirésuperlattice provides a pathway for the realization of artificial excitonic crystals.Here we systematically summarize the current achievements in twistronics and moiréexcitonic physics,with emphasis on the roles of lattice rotational mismatches and atomic registries.Firstly,we review the effects of the interlayer twist on electronic and photonic physics,particularly on exciton properties such as dipole moment and spin-valley polarization,through interlayer interactions and electronic band structures.We also discuss the exciton dynamics in vdW heterostructures with different twist angles,like formation,transport and relaxation processes,whose mechanisms are complicated and still need further investigations.Subsequently,we review the theoretical analysis and experimental observations of moirésuperlattice and moirémodulated excitons.Various exotic moiréeffects are also shown,including periodic potential,moiréminiband,and varying wave function symmetry,which result in exciton localization,emergent exciton peaks and spatially alternating optical selection rule.We further introduce the expanded properties of moirésystems with external modulation factors such as electric field,doping and strain,showing that moirélattice is a promising platform with high tunability for optoelectronic applications and in-depth study on frontier physics.Lastly,we focus on the rapidly developing field of correlated electron physics based on the moirésystem,which is potentially relate
The past few years have witnessed prominent progress in two-dimensional(2D)van der Waals heterostructures.Vertically assembled in an artificial manner,these atomically thin layers possess distinctive electronic,magnetic,and other properties,which have provided a versatile platform for both fundamental exploration and practical applications in condensed matter physics and materials science.Within various potential combinations,a particular set of van der Waals superconductor(SC)heterostructures,which is realized by stacking fabrication based on two-dimensional SCs,is currently attracting intense attention.For example,the Josephson junction,a specific structure in which a nonsuperconducting barrier is inserted between two proximity-coupled SCs,shows phenomena and outstanding properties with atomic-scale thickness.In this Perspective,we first review this emerging research area of van der Waals SC heterostructures,especially progress on the 2D van der Waals Josephson junctions,from the aspects of preparation,performance,and application,and also propose our vision for the future direction and potential innovation opportunities.
