Spin-orbit coupling-enhanced valley ordering of malleable bands in twisted bilayer graphene on WSe2

Recent experiments in magic-angle twisted bilayer graphene have revealed a wealth of novel electronic phases as a result of interaction-driven spin-valley flavour polarisation. In this work, we investigate correlated phases due to the combined effect of spin-orbit coupling-enhanced valley polarisation and the large density of states below half filling of the moire band in twisted bilayer graphene coupled to tungsten diselenide. We observe an anomalous Hall effect, accompanied by a series of Lifshitz transitions that are highly tunable with carrier density and magnetic field. The magnetisation shows an abrupt change of sign near half-filling, confirming its orbital nature. While the Hall resistance is not quantised at zero magnetic fields-indicating a ground state with partial valley polarisation-perfect quantisation and complete valley polarisation are observed at finite fields. Our results illustrate that singularities in the flat bands in the presence of spin-orbit coupling can stabilise ordered phases even at non-integer moire band fillings. Twisted bilayer graphene hosts a zoo of rich correlated electronic phases. Here, the authors explore the phase diagram of a twisted bilayer graphene/tungsten diselenide heterostructure and uncover a series of delicate Fermi surface reconstructions and signatures of orbital magnetism.

Automated summary

Recent experiments in magic-angle twisted bilayer graphene have revealed a variety of novel electronic phases due to interaction-driven spin-valley flavour polarisation. In this work, the authors investigate correlated phases in twisted bilayer graphene coupled to tungsten diselenide, resulting from spin-orbit coupling-enhanced valley polarisation and large density of states below half filling of the moire band. They observe an anomalous Hall effect and tuneable Lifshitz transitions, as well as revealing the orbital nature of magnetisation near half filling. The Hall resistance shows quantisation and complete valley polarisation at finite fields, indicating the stabilisation of ordered phases at non-integer moire band fillings.