| Citation | Distinguished for his work on theoretical magnetism and on the theory of the fractional quantum Hall effect. His solution of the Anderson model of local moments had great influence on the theory of mixed valence materials. His work on the difference between the excitation of spin chains with integer and half-integer spins upset many preconceptions, and is now regarded as of great importance. He argued that in one case there should be a gap, while in the other case the spectrum should continue down to zero. His theory of the hierarchical structure of the fractions at which the fractional quantum Hall effect is observed has been important. His ingenious study of the fractional quantum Hall effect on a spherical surface opened the way to a more careful and elegant treatment than was previously available. It also provided an unexpected link with the nuclear shell model. His original insights into a variety of problems have stimulated advances in quntum field theory as well as in condensed matter physics. |