3:30–4:30 pm Maria Goeppert-Mayer Lecture Hall
Using topology to build "impossible" electronic devices in graphene heterostructures
Andrea Young, University of California, Santa Barbara
Since the discovery of quantized Hall effects in the 1980s, topology has provided a useful new paradigm for understanding condensed matter systems, expanding our vocabulary for describing the distinctions between states of matter. I will focus on how topological properties can be harnessed to build otherwise impossible electronic devices--devices whose operation, in turn, provides precise tests of the topological description of matter. In the first example, I will show how a quantized Hall effect can be realized at zero magnetic field from the spontaneous alignment of orbital magnetic moments in a graphene heterostructure where a moire pattern generates an artificial superlattice. Remarkably, the large magnetic moments of the chiral edge resulting chiral edge states can be used to realize an electrically actuated magnetic memory, where the macroscopic magnetic moment can be controllably reversed through the application of electrostatic potential. In the second example, I will show how the fractionalization of charge characteristics of topologically ordered states can be used to realize a purely direct current voltage step-up transformer. Along the way, I will introduce the physics of van der Waals heterostructures, layered stacks of atomically thin two-dimensional crystals, and show how the remarkable experimental control available in these systems has made them the leading platform for exploring the interplay of topology and many-body quantum physics.