Optical control of slow topological electrons in moiré systems

A fundamental feature of magic-angle twisted bilayer graphene is the presence of flat-electron bands with extremely low electron velocities. These flat bands appear over an even wider range of twist angles in periodically driven (Floquet) twisted bilayer graphene (TBG) [1-3] and allow phonon speeds to exceed that of electrons [7]. We show that the optically induced flat bands in THz laser driven TBG enable electrons carrying large Berry curvature to decouple from acoustic phonons. The resulting light-induced Hall response [4-6] exhibits sharp changes as a function of the laser amplitude. Our work suggests that the unique light-induced topological and transport physics in Floquet TBG are experimentally accessible and can be observed using simple experimentally available probes. We will discuss generalizations to UV-visible (high-frequency) laser-driven TBG, where the steady-state formation relies on an avalanche of scattering processes between many highly dispersive bands and the flat bands.



[1] Katz, O., Refael, G., Linder, N.H. PRB (2020)

[2] Y. Li, H. A. Fertig, and B. Seradjeh, PRR (2020)

[3] G. E. Topp, et al., PRR 1 (2019)

[4] J. W. McIver, et al., Nature Physics (2020)

[5] S. A. Sato, et al., PRB (2019)

[6] T. Oka and H. Aoki, PRB (2009)

[7] I. Esin, I. Esterlis, E. Demler, and G. Refael, (2022)