Physics Colloquium
Orbital Chern insulators in flat-band graphene moiré systems
Dr. Hryhoriy Polshyn
Postdoctoral Scholar, Department of Physics
University of California Santa Barbara
Taming topological electronic phases is one of the central problems of modern condensed matter physics and a prerequisite for new technologies such as topological quantum computation. Realizing topological phases at zero magnetic field has been a longstanding goal since Haldane’s theoretical proposal of the quantum anomalous Hall (QAH) state. My talk will focus on newly discovered QAH states that emerge in twisted bilayer and trilayer graphene systems. In contrast to magnetically doped topological insulators, the QAH states in these moiré systems are driven by intrinsic strong interactions, which polarize the electrons into a single moiré miniband with Chern number of C = 1 or 2. Remarkably, the magnetization of these “orbital Chern insulators” (OCI) arises predominantly from the orbital motion of the electrons rather than the electron spin. I will discuss a novel effect originating from the curious magnetic properties of OCIs that enables non-volatile electrical switching of the magnetic and topological orders. Finally, I will present recent studies of the OCIs that emerge at half-fillings of moiré minibands and spontaneously break the moiré superlattice symmetry.
All interested persons are invited to attend remotely—email physics@nd.edu for information.