Photocurrents as correlated phase indicators in twisted bilayer graphene

The competition between many correlated phases within a narrow energy range in magic angle twisted bilayer graphene (TBG) makes the task of diagnosing the ground state as a function of filling challenging. Photogalvanic effects that access the geometrical properties of the band structure, can be a promising tool to experimentally distinguish symmetry broken phases. In this work, by using a heavy fermion description for TBG [1], we perform self-consistent calculations for the second order optical responses associated to the spontaneous symmetry-broken states mainly arising from the local interaction between the heavy electrons. These optical responses can be used to obtain a wealth of information about the correlated ground states in TBG as a function of filling. The comparison of our predictions with experiments can serve to constrain the theoretical modelling of correlated phenomena in TBG.

[1] Song, Z.-D. & Bernevig, B. A. Magic-angle twisted bilayer graphene as a topological heavy fermion problem. Phys. Rev. Lett. 129, 047601 (2022).