The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics 2016 with one half to David J. Thouless University of Washington, Seattle, WA, USA and the other half to F. Duncan M. Haldane Princeton University, NJ, USA and J. Michael Kosterlitz Brown University, Providence, RI, USA
”for theoretical discoveries of topological phase transitions and topological phases of matter”
This year’s Laureates opened the door on an unknown world where matter can assume strange states. They have used advanced mathematical methods to study unusual phases, or states, of matter, such as superconductors, superfluids or thin magnetic films. Thanks to their pioneering work, the hunt is now on for new and exotic phases of matter. Many people are hopeful of future applications in both materials science and electronics.
The three Laureates’ use of topological concepts in physics was decisive for their discoveries. Topology is a branch of mathematics that describes properties that only change step-wise. Using topology as a tool, they were able to astound the experts. In the early 1970s, Michael Kosterlitz and David Thouless overturned the then current theory that superconductivity or suprafluidity could not occur in thin layers. They demonstrated that superconductivity could occur at low temperatures and also explained the mechanism, phase transition, that makes superconductivity disappear at higher temperatures.
In the 1980s, Thouless was able to explain a previous experiment with very thin electrically conducting layers in which conductance was precisely measured as integer steps. He showed that these integers were topological in their nature. At around the same time, Duncan Haldane discovered how topological concepts can be used to understand the properties of chains of small magnets found in some materials.
We now know of many topological phases, not only in thin layers and threads, but also in ordinary three-dimensional materials. Over the last decade, this area has boosted frontline research in condensed matter physics, not least because of the hope that topological materials could be used in new generations of electronics and superconductors, or in future quantum computers. Current research is revealing the secrets of matter in the exotic worlds discovered by this year’s Nobel Laureates.
What are phase transitions?
Phase transitions refer to abrupt changes in the properties of a material - for instance the progression from ice to water to steam as the temperature is ramped up from freezing. However, as well as the traditional states of solid, liquid, gas, Thouless, Haldane and Kosterlitz (and others) showed that materials also make sudden transitions in their electrical properties. This might manifest itself as a sudden drop in the electrical resistance of a material as it is cooled down. So-called topological phase transitions were initially investigated in materials with thin layers, or ones that formed thin threads, but now scientists have shown that “exotic” electrical properties can be found in a wide range of materials.
