Orbital Multiferroicity in Twist Monolayer–Bilayer Graphene

Abstract

Owing to their electrically tunable nature, orbital ferroic orders have attracted intense interests and possess great potential for applications in next-generation electronic devices. Systems hosting coexisting multiple orbital ferroic orders, namely, orbital multiferroicity, have emerged as promising platforms to probe the interplay between these orders, yet it remains largely unexplored. Herein, we report the orbital multiferroicity and the intriguing competitive behavior between different orbital ferroic orders in twisted monolayer–bilayer graphene (tMBG), which facilitates the attainment of multidimensional control. At three electrons per moiré unit cell, two distinct orbital ferroic orders, that is, orbital ferromagnetic and ferro-valleytronic orders, emerge and exhibit a competitive relation. Under low magnetic fields, the orbital ferromagnetic energy dominates the electronic free energy and results in hysteretic transitions triggered by magnetic field and carrier density. However, with increasing magnetic field, the orbital ferro-valleytronic energy becomes comparable to the orbital ferromagnetic energy, inducing additional transitions driven by magnetic fields and electrical displacement fields. Our findings highlight the potential of orbital multiferroicity for enabling multidimensional control in nonvolatile information storage devices.