Superconductivity in twisted Graphene ${\rm NbSe_2}$ heterostructures

Abstract

We study the low-energy electronic structure of heterostructures formed by one sheet of graphene placed on a monolayer of ${\rm NbSe_2}$. We build a continuous low-energy effective model that takes into account the presence of a twist angle between graphene and ${\rm NbSe_2}$, and of spin-orbit coupling and superconducting pairing in ${\rm NbSe_2}$. We obtain the parameters entering the continuous model via ab-initio calculations. We show that despite the large mismatch between the graphene's and ${\rm NbSe_2}$'s lattice constants, due to the large size of the ${\rm NbSe_2}$'s Fermi pockets, there is a large range of values of twist angles for which a superconducting pairing can be induced into the graphene layer. In addition, we show that the superconducting gap induced into the graphene is extremely robust to an external in-plane magnetic field. Our results show that the size of the induced superconducting gap, and its robustness against in-plane magnetic fields, can be significantly tuned by varying the twist angle.