Physics Colloquium - McMillan Award Winner - Jiaqi Cai 10/22/2025

Title: “Fractional quantum anomalous Hall effect in twisted MoTe₂: discovery and recent advances”

Abstract: Condensed matter physics seeks to understand the collective behavior of particles, which often manifest as quasiparticles. The principle of fractionalization, in particular, uncovers exotic particles with no Standard Model counterpart, such as anyons. A seminal example is the fractional quantum Hall effect (FQHE), where electrons in a 2D gas form quasiparticles with fractional charge and anyonic statistics under an extreme magnetic field and low temperature. However, these stringent experimental conditions pose significant challenges for manipulating and probing these exotic states.

This talk will present the discovery and recent advances in the fractional quantum anomalous Hall effect (FQAHE), a lattice analog of the FQHE that emerges in the topological flat bands of twisted MoTe₂ at zero magnetic field and at possibly elevated temperatures using combined optical spectroscopy and transport measurement. The less stringent experimental conditions enable the application of novel experimental probes previously incompatible/hard with FQHE systems. We will focus on recent progress using these new techniques, including the possible detection of charge-neutral spin excitations with novel device design, which could provide new insights into the nature of anyonic physics in this strongly correlated platform.