Electronic steady states of Floquet moiré materials

A fundamental feature of magic angle twisted bilayer graphene is the presence of flat-electron bands with extremely low Fermi velocities. These flat bands appear over an even wider range of twist angles in periodically-driven (Floquet) twisted bilayer graphene (TBG) [1]. Such flat bands enable a new regime of electron dynamics wherein the acoustic phonon speeds c exceed that of electrons v [2]. In this work, we study a TBG periodically driven with a resonant low-frequency drive. We discuss the conditions under which coupling to a heat bath of phonons leads to low-entropy electronic steady states and how the competition in electron and phonon speeds affects the nature of these steady-states in nearly flat-band systems. In particular, we find that in the fast phonon regime (c > v), the steady state exhibits unusual features in the distribution of electrons and holes away from the resonance condition. We will discuss the origins of these features and demonstrate how these may be detected experimentally.

[1] Katz, O., Refael, G., Linder, N.H. “Optically induced flat bands in twisted bilayer graphene.” Phys. Rev. B 102, 155123 (2020).

[2] Mikito Koshino and Young Woo Son. “Moire phonons in twisted bilayer graphene.” Phys. Rev. B 100, 075416 (2019).