David Thouless

David Thouless (born September 21, 1934, Bearsden, Scotland—died April 6, 2019, Cambridge, England) was a British-born American physicist who was awarded the 2016 Nobel Prize in Physics for his work on using topology to explain superconductivity and the quantum Hall effect in two-dimensional materials. He shared the prize with British-born American physicists Duncan Haldane and Michael Kosterlitz.

Thouless received a bachelor’s degree from the University of Cambridge in 1955 and a doctorate in theoretical physics in 1958 from Cornell University. He was a physicist at Lawrence Berkeley National Laboratory from 1958 to 1959 and then was a research fellow at the University of Birmingham until 1961. He returned to Cambridge and was a lecturer until 1965 and was a professor of mathematical physics at Birmingham from 1965 to 1978. After being a professor of applied science at Yale University from 1979 to 1980, he went to the University of Washington, Seattle, as a professor of physics and became an emeritus professor in 2003.

In the early 1970s, when Thouless and Kosterlitz were at Birmingham together, they became interested in phase transitions in two dimensions. Phase transitions happen when a material changes from one ordered type of matter to another; the melting of ice is a phase transition because the water changes from one phase (solid ice) to another (liquid water). In two dimensions, it was believed, random thermal fluctuations would make any kind of order and thus any kind of phase transition impossible. If there were no phase transitions, phenomena like superfluidity and superconductivity could not occur. Thouless and Kosterlitz discovered a topological phase transition in which, at cold temperatures, spinning vortices would form in closely separated pairs and, as the temperature increased, the material would enter another phase in which the vortices split apart and travel freely. This transition is known as the Kosterlitz-Thouless (KT) transition (or sometimes the Berezinskii-Kosterlitz-Thouless [BKT] transition).

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In 1983 Thouless also used topology to explain the quantum Hall effect, in which, when a thin conducting layer is placed between two semiconductors and cooled to near absolute zero (−273.15 °C [−459.67 °F]), the electrical resistance of the conductor changes in discrete steps as a magnetic field varies. In fact, the inverse of the electrical resistance, called the conductance, varies in integer steps. He found that the conductance followed a kind of integer known from topology as the Chern number. This work was later extended by Haldane to show that such effects that were dependent on the Chern number could occur even without a magnetic field.