Niels Bohr Lecture by Andrea Young, University of California

Topology, correlations, and “impossible” electronic devices in graphene heterostructures

Abstract: 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 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 a electrostatic potential.

In the second example, I will show how the fractionalization of charge characteristic 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. 

About the speaker

Andrea Young received his PhD from Columbia University in 2012.  Following a Pappalardo Fellowship at MIT and stint as a visiting scientist at Weizmann Institute, he began his research group at UC Santa Barbara in 2015. 

His research career has focused on the development of "van der Waals heterostructures" - interleaved sheets of two dimensional atomic layers - and using them as a platform to reveal the nature of collective states of electronic matter in two dimensions. 

Besides nanofabrication and quantum transport techniques, his group has also specialized in ultra-sensitive magnetic scanned probes based on nanoscale superconducting quantum interference devices.  

Coffee, tea and cake will be served outside Aud. 3 at 15:45