Career
He is the Robert West. Reneker Distinguished Service Professor in the Department of Physics at the University of Chicago, James Franck Institute and Enrico Fermi Institute. He specializes in theoretical condensed matter physics. He made pioneering contributions to the field of quantum integrable systems
He found exact solutions of O(3) Non-linear Sigma Model, (Wiegmann 1985), Wess–Zumino–Witten model (together with Alexander Polyakov), Anderson impurity model and Kondo model.