Speaker: Ashely Cook, Max Planck Institutes for the Physics of Complex Systems and the Chemical Physics of Solids
Abstract: In the quantum Hall effect, a two-dimensional gas of electrons is subjected to an out-of-plane magnetic field and electron transport quantises: the Hall conductivity plateaus at values proportional to integers and rational numbers in units of fundamental constants, with remarkably low error. Shortly after experimental discovery of the quantum Hall effect in 1980, theorists developed a framework explaining this quantization as a consequence of topological phases of matter, or those phases with signatures unaffected by sufficiently small perturbations. In particular, a theory in terms of point charges coupling to external fields beautifully described this physics. A great variety of topological phases have been classified as a consequence of discovery of the quantum Hall effect, but this work has recently led to discovery of topological skyrmion phases of matter, multiplicative topological phases of matter, and finite-size topological phases of matter, which contradict key assumptions of established classification schemes. The discovery of these three sets of topological states necessitates a paradigm shift from the quantum Hall effect framework to that of the quantum skyrmion Hall effect, in which the point charges of the quantum Hall effect are generalised to truly quantum counterparts of topological textures in observable fields, called skyrmions.