Magnetic injection photocurrents in valley-polarized states of twisted bilayer graphene
Phys. Rev. B 113, 035443 – Published 28 January, 2026
DOI: https://doi.org/10.1103/1zsf-kh2q
Abstract
Magic-angle twisted bilayer graphene displays a complex phase diagram as a function of flat-band filling, featuring compressibility cascade transitions and a variety of competing ground states with broken spin, valley, and point-group symmetries. Recent terahertz photocurrent spectroscopy experiments have shown a dependence on the filling, which is not consistent with the simplest cascade picture of sequential filling of equivalent flat bands. In this work, we show that when time-reversal symmetry is broken due to valley polarization, a magnetic injection photocurrent develops, which can be used to distinguish different spin-valley polarization scenarios. Using the topological heavy fermion model, we compute both shift and injection currents as a function of filling. We argue that current experiments can be used to determine the spontaneous valley polarization.
