Applied Physics and Materials Science Seminar Series
***Refreshments at 4:00pm in Noyes Lobby
Abstract:
Microscopy has made states of matter visible as spatial objects, revealing where domains nucleate, how phase boundaries move, and when conducting pathways connect. Yet quantitative measures of this organization remain limited. In this talk, I will discuss two new approaches that extend the information accessible through the microscopy of quantum materials. First, I will describe layer-resolved microwave impedance microscopy, a technique that images quantum electronic states on individual atomic planes within van der Waals heterostructures at temperatures down to 50 mK. Applied to double-layer graphene, this technique reveals how charge disorder varies between layers and how electrostatic screening influences fragile fractional quantum Hall states.
Drawing upon the toolbox of information theory, I will next introduce "algorithmic entropy imaging," a technique that uses lossless data compression to quantify spatial complexity, predictability, and hidden order in microscopy images of materials. Repeated motifs can be encoded compactly, while less predictable patterns require longer descriptions. In graphene, this technique reveals a pronounced maximum in spatial complexity near the quantum Hall critical point, where isolated conducting regions evolve into an extended network. Applied to other imaging modalities, the same approach tracks evolving spatial complexity in magnetic skyrmion textures and wrinkle networks in growing bacterial biofilms, offering a portable probe of spatial organization in systems ranging from quantum materials to living matter.
More about the Speaker:
Monica Allen is an Assistant Professor of Physics at the University of California, San Diego. Her research combines scanning probe microscopy, electronic transport, and nanofabrication to investigate correlated and topological states in quantum materials. Her group develops microwave imaging techniques that operate at millikelvin temperatures to visualize electronic phases and their spatial organization. She received her B.A. and Ph.D. in Physics from Harvard University and was a Karel Urbanek Postdoctoral Fellow in Applied Physics at Stanford University before joining UC San Diego. She is a recipient of the NSF CAREER Award and the Air Force Office of Scientific Research Young Investigator Award.