Bertrand I. Halperin is the Hollis Professor of Mathematicks and Natural Philosophy, Emeritus, at Harvard University. He was born in Brooklyn, New York, on December 6, 1941. Both his parents had been born in the Ukraine but had moved to the United States as children. Halperin received his AB degree from Harvard in 1961, and his PhD from the University of California, Berkeley, in 1965. Following a postdoctoral year in Paris, he spent ten years at Bell Laboratories, and then joined the Harvard physics faculty in 1976.
Halperin's research interests have concerned many aspects of the theory of condensed matter systems and statistical physics. At Bell laboratories, a major portion of his work was focused on dynamic phenomena at a classical critical point, i.e., transport properties and time-dependent correlations near a phase transition with diverging correlation length. Together with Pierre Hohenberg and other collaborators, he developed a scheme for classifying dynamic behavior at different type of critical points and showed how the recently-developed renormalization group methods could be extended to calculate quantities such as critical exponents for dynamic properties.
At Harvard, together with David Nelson, Halperin developed a theory of melting in two dimensions, which showed that under appropriate conditions, melting could occur in two stages, with a liquid-crystal phase occurring between the solid and the liquid. This phase, which they termed “hexatic”, would have only short-range translational order but quasi-long-range bond-orientation order, with six-fold symmetry.
A major focus of Halperin’s work since 1981 has been on quantum Hall effects, the various peculiar phenomena that can occur in two-dimensional electron systems in strong magnetic fields at low temperatures. In early work, Halperin pointed out that quantized Hall systems necessarily had conducting states at their boundaries, and these states were crucial for understanding the exactness of the quantized Hall conductance in physical systems. In later work, he showed that quasiparticles in fractional quantized Hall systems do not behave as fermions or bosons but rather obey fractional statistics, a phenomenon that had earlier been proposed as a mathematical possibility in two-dimensional systems but had not been known to occur in any actual system. In the early 1990s, together with Patrick Lee and Nicholas Read, Halperin developed a theory of the quantum state at Landau-level filling ½, where there is no quantized Hall conductance, but a number of other peculiar properties are observed.
Over the years, Halperin has made contributions in various other areas, including one-dimensional metals, quantum antiferromagnets in one and two dimensions, low-temperature properties of glasses, and transport in inhomogeneous media.
Halperin is a member of the U. S. National Academy of Sciences and the American Philosophical Society, and a fellow of the American Academy of Arts and Sciences and the American Physical Society. His awards include the Buckley Prize and the Onsager Prize from the APS, the Dannie Heineman Prize of the Göttingen Akademie der Wissenschaften, the Lars Onsager Lecture and Medal of the Norwegian University of Science and Technology, an honorary doctorate from the Weizmann Institute of Science, the Lise Meitner Lecture and Medal, the 2019 APS Medal for Exceptional Achievement in Research, and the Wolf Prize in Physics.