Twist-angle dependent pseudo-magnetic fields in monolayer CrCl2/graphene heterostructures.

The generation of pseudo-magnetic fields in strained graphene leads to quantized Landau levels in the absence of an external magnetic field, providing the potential to achieve a zero-magnetic-field analogue of the quantum Hall effect. Here, we report the realization of a pseudo-magnetic field in epitaxial graphene by building a monolayer CrCl₂/graphene heterointerface. The CrCl₂ crystal structure exhibits spontaneous breaking of three-fold rotational symmetry, yielding an anisotropic displacement field at the interface. Using scanning tunneling spectroscopy, we have discovered a sequence of pseudo-Landau levels associated with massless Dirac fermions. A control experiment performed on the CrCl₂/NbSe₂ interface confirms the origin as the pseudo-magnetic field in the graphene layer that strongly interacts with CrCl₂. More interestingly, the strength of the pseudo-magnetic fields can be tuned by the twist angle between the monolayer CrCl₂ and graphene, with a variation of up to threefold, depending on the twist angle of 0° to 30°. This work presents a rare 2D heterojunction for exploring PMF-related physics, such as the valley Hall effect, with the advantage of easy and flexible implementation.