Hall conductance as a topological invariant of gapped states of matter

Quantum Hall Effect is one of the most studied phenomena in solid state physics. For systems of non-interacting electrons, there is a satisfactory mathematical theory of QHE. Over the last few years, its counterpart for interacting systems has been developed. It is based on the assumption that there is a energy gap for bulk excitations. I will sketch a version of this theory which applies to infinite-volume systems and shows that the Hall conductance at zero temperature is a homotopy invariant of gapped U(1)-invariant systems in 2d spatial dimensions. Within this approach, generalizations to non-abelian symmetry groups and higher dimensions is straightforward. 

Please note the special time (17:00) due to the time difference between Israel and California.

This is a Zoom only lecture: https://technion.zoom.us/j/99989546990