David Thouless coauthored a theory connecting the Hall conductivity of a two-dimensional electron gas to a topological invariant. In a uniform magnetic field and periodic potential, the Kubo formula can be written so that quantization becomes explicit when the Fermi energy lies in a gap. The integer character of the response explains why continuous changes of microscopic parameters need not continuously change the Hall plateau. A transition between distinct plateaus requires leaving the conditions that protect that quantization.[ref]
Quantized Hall Conductance in a Two-Dimensional Periodic Potential by D. J. Thouless and others. Physical Review Letters 49, 405 (1982), abstract and topological conductance expression
A physicist who researched superfluidity and superconductivity in thin systems.[ref]
David Thouless — Nobel laureate and UW professor emeritus — dies at age 84 by University of Washington. Independent professional identity
Portrait of David Thouless
. Mary Levin/University of Washington. CC BY-SA 4.0, via Wikimedia Commons. Source.
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