Xiaodong Xu – University of Washington
Title: Observation of Fractional Quantum Anomalous Hall Effect

Abstract: The interplay between spontaneous symmetry breaking and topology can result in exotic quantum states of matter. A celebrated example is the quantum anomalous Hall (QAH) state, which exhibits an integer quantum Hall effect at zero magnetic field due to topologically nontrivial bands and intrinsic magnetism. In the presence of strong electron-electron interactions, fractional-QAH (FQAH) states at zero magnetic field can emerge, which is a lattice analog of fractional quantum Hall effect without Landau level formation. In this talk, I will present experimental observation of FQAH states in twisted MoTe2 bilayer, using combined magneto-optical and -transport measurements. In addition to the Chern number -1 integer, and -2/3 and -3/5 fractional QAH states, we find an anomalous Hall state near the filling factor -1/2, whose behavior resembles that of the composite Fermi liquid in the half-filled lowest Landau level of a two-dimensional electron gas at high magnetic field. Direct observation of the FQAH and associated effects paves the way for researching charge fractionalization and anyonic statistics at zero magnetic field.

Speaker bio: Xiaodong Xu is a Boeing Distinguished Professor in the Department of Physics, and Department of Materials Science and Engineering at the University of Washington. He obtained a PhD in Physics from the University of Michigan in 2008. After postdoc research at Cornell University, he joined the University of Washington in 2010. He is a Fellow of American Physical Society and Optical Society of America.