Realization of asymmetric spin splitting Dirac cones in antiferromagnetic graphene/CrAs2/graphene heterotrilayer.

Nonmagnetic graphene-based van der Waals heterotrilayers exhibit peculiar electronic features such as energetically and/or spatially resolved Dirac rings/cones. Here, using first-principles calculations we study the effect of magnetic proximity effect and mirror symmetry of antiferromagnetic CrAs2 monolayer sandwiched between graphene on the Dirac cones. We clearly identify the common vertical shift of the Dirac bands in the spin up channel. While in the spin down channel, we surprisingly observe the remarkable transverse splitting Dirac cones. The underling mechanism can be attributed to the static electric field caused by the charge transfer between the interlayers, and the polarized field arising from the weakly magnetized graphene. Both fields collectively give rise to an inequivalent space inversion broken between graphene and CrAs2 layers. Such unique Dirac states are absent in its nonmagnetic or ferromagnetic counterpart, ferromagnetic heterotrilayer with the glide symmetry, and graphene/CrAs2 heterobilayer. Our findings would provide a new insight into the correlation between Dirac cones and magnetic monolayer sandwiched between graphene.

Reversible direct-indirect band transition in alloying TMDs heterostructures via band engineering.

Alloying is a feasible and practical strategy to tune the electronic properties of 2D layered semiconductors. Here, based on first-principles calculations and analysis, we demonstrate band engineering through alloying W into a prototype MoS2/MoSe2 heterostructure. Especially, when the W compositions x > 0.57 in Mo1-x W x S2/MoSe2, it exhibits remarkable and reversible direct- to indirect-gap transition. This is because for Mo1-x W x S2/MoSe2, the valence band maximum located at the K point originates from dominant MoSe2, while the competing Γ state stems from the hybridization of both Mo1-xW x S2 and MoSe2, which is extremely sensitive to the interlayer coupling. Consequently, alloying in MoS2 layer induces direct- to indirect-gap transition and gap increase due to the weakened p-d coupling. We also observe that whether initial alloying in MoS2 or MoSe2, the µMo-µW poor condition should always be used. Our findings are generally applicable and will significantly expand the band engineering to other alloying TMDs heterostructures.