Seminar: Three-dimensional quantized Hall effect from Weyl orbit & Machine Learning in Electronic Quantum Matter Imaging Experiments

Time:        3pm, April 16, 2019 (Tuesday)

Place:        East Bulg. 4, Room 242, Zijingang Campus

 

Abstract:

Discovered decades ago, the quantum Hall effect remains one of the most studied phenomena in condensed matter physics. Here we report a new type of quantum Hall effect based on Weyl orbit that consists of Fermi arc surface states on opposite surfaces of the sample connected by one-dimensional chiral Landau levels through the bulk and extends the quantum Hall effect to higher dimensions without simply stacking two-dimensional systems. The corresponding Landau levels and the quantum Hall transport are strongly modulated by both the sample thickness and the magnetic field, and exotic chiral states can emerge even in the bulk. We show evidence of exploring this quantum Hall physics in three-dimensional materials with enhanced tunability in transport experiments using nanostructures of the three-dimensional topological semimetal Cd3As2 with variable thickness.

Today, we face major scientific challenges because automated scientific instrumentation and large-scale data acquisition have revolutionized empirical science by generating data of such volume and complexity as to defy human analysis. Here we report development in machine learning approaches and artificial neural networks in recognizing different types of hypothesized order hidden in complex electronic quantum matter images at the atomic scale. As a demonstration, we analyze a large, experimentally-derived electronic quantum matter image archive spanning a wide
range of electron densities and energies in carrier-doped cuprates. Remarkably, throughout all the instrumentally noisy and intrinsically chaotic data we repeatedly and reliably discover a very specific, lattice-commensurate, unidirectional, and translational-symmetry-breaking state that has long been predicted by particle-like strong-coupling theories of electronic liquid crystals. 

References: Quantum Hall effect based on Weyl orbits in Cd3As2, Cheng Zhang*, YZ*, Xiang Yuan*, et al., Nature 565, 331–336 (2019); Machine Learning in Electronic Quantum Matter Imaging Experiments YZ*, A. Mesaros*, et al., Nature (accepted, in production) (2019); eprint-arXiv: 1808.00479.

 

Biography:

Dr. Zhang, Yi is a theoretical condensed matter physicist focusing on emergent phenomena and novel approaches in quantum materials and systems. He obtained his Ph.D. degree at UC Berkeley under Prof. Ashvin Vishwanath. Then he moved to Stanford University as a SITP postdoctoral fellow and later to Cornell University as a Bethe fellow. Just now, he joined the International Center for Quantum Materials and the School of Physics at Peking University as a junior faculty member. Yi Zhang is interested in machine learning and quantum entanglement applications in quantum materials, theoretical characterizations and experimental properties of topological phases and materials, and various other topics.  Dr. Zhang, Yi has published more than 30 papers with more than 1800 times’ citations, including publications in Nature, Nature Physics, PRL, Nature communications and Nano Lett.etc.