Intrinsic non-magnetic $\phi_0$ Josephson junctions in twisted bilayer graphene

Abstract

Recent experiments have demonstrated the possibility to design highly controllable junctions on magic angle twisted bilayer graphene, enabling the test of its superconducting transport properties. We show that the presence of chiral pairing in such devices manifests in the appearance of an anomalous Josephson effect ($\phi_0$ behavior) even in the case of symmetric junctions and without requiring any magnetic materials or fields. Such behavior arises from the combination of chiral pairing and nontrivial topology of the twisted bilayer graphene band structure that can effectively break inversion symmetry. Moreover, we show that the $\phi_0$ effect could be experimentally enhanced and controlled by electrostatic tuning of the junction transmission properties.