Bulk cadmium arsenide (Cd3As2) hosts topologically non-trivial bands in its electronic structure. In thin films, it can be engineered to a variety of new topological phases. In this talk, we will discuss topological and correlated insulator states in high-quality quantum wells of Cd3As2, which we grow by molecular beam epitaxy. Using Landau level spectroscopy, we show that the films transition to a two-dimensional topological insulator phase at quantum well thicknesses around 20 nm. At lower thicknesses, the topological gap closes and reopens as a trivial gap. An in-plane Zeeman magnetic field induces a topological phase transition to a 2D Weyl semimetal phase, which shows a well-developed odd-integer quantum Hall effect under a small perpendicular magnetic field. We show that new types of insulators appear near the critical thickness. Using transport measurements, we identify these new insulators as hole and electron Wigner solids, respectively, that form spontaneously at zero magnetic field. Hysteresis and voltage fluctuations point to domain motion across the pinning potential and disappear at finite temperature as thermal fluctuations overcome the potential. We discuss the interplay of topology, electron correlations, and spin-orbit coupling that gives rise to these novel insulating states.
Bio: Susanne Stemmer is Professor of Materials at the University of California, Santa Barbara. She did her doctoral work at the Max-Planck Institute for Metals Research in Stuttgart (Germany) and received her degree from the University of Stuttgart. Her current research interests include scanning transmission electron microscopy techniques, molecular beam epitaxy, and topological materials. Honors include election to Fellow of the American Ceramic Society, Fellow of the American Physical Society, Fellow of the Materials Research Society, Fellow of the Microscopy Society of America, and a Vannevar Bush Faculty Fellowship of the U.S. Department of Defense.
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2026-01-15T10:00:002026-01-15T11:00:00Topological and Correlated Phases in Thin Films of Cadmium ArsenideEvent Information:
Bulk cadmium arsenide (Cd3As2) hosts topologically non-trivial bands in its electronic structure. In thin films, it can be engineered to a variety of new topological phases. In this talk, we will discuss topological and correlated insulator states in high-quality quantum wells of Cd3As2, which we grow by molecular beam epitaxy. Using Landau level spectroscopy, we show that the films transition to a two-dimensional topological insulator phase at quantum well thicknesses around 20 nm. At lower thicknesses, the topological gap closes and reopens as a trivial gap. An in-plane Zeeman magnetic field induces a topological phase transition to a 2D Weyl semimetal phase, which shows a well-developed odd-integer quantum Hall effect under a small perpendicular magnetic field. We show that new types of insulators appear near the critical thickness. Using transport measurements, we identify these new insulators as hole and electron Wigner solids, respectively, that form spontaneously at zero magnetic field. Hysteresis and voltage fluctuations point to domain motion across the pinning potential and disappear at finite temperature as thermal fluctuations overcome the potential. We discuss the interplay of topology, electron correlations, and spin-orbit coupling that gives rise to these novel insulating states.
Bio: Susanne Stemmer is Professor of Materials at the University of California, Santa Barbara. She did her doctoral work at the Max-Planck Institute for Metals Research in Stuttgart (Germany) and received her degree from the University of Stuttgart. Her current research interests include scanning transmission electron microscopy techniques, molecular beam epitaxy, and topological materials. Honors include election to Fellow of the American Ceramic Society, Fellow of the American Physical Society, Fellow of the Materials Research Society, Fellow of the Microscopy Society of America, and a Vannevar Bush Faculty Fellowship of the U.S. Department of Defense. Event Location:
BRIM 311