24 October 2016 2016 Nobel Prize in Physics

Professors Maciej Lewenstein and Adrian Bachtold

Professors Maciej Lewenstein and Adrian Bachtold offer a special colloquium to discuss the importance of the topic and its implications On Tuesday, 4th October, three British scientists, David J. Thouless, F. Duncan M. Haldane and J. Michael Kosterlitz were awarded the Nobel Prize in Physics for theoretical discoveries of topological phase transitions and topological phases of matter. The importance of this topic is well known for researchers at ICFO as it is a focus area shared by various research groups at our institute.

ICREA Prof. at ICFO Maciej Lewenstein and ICFO Prof. Adrian Bachtold, both of whom lead vigorous in-house research programs that have a significant overlap with the topic awarded the Nobel Prize, offered a colloquium on the importance and implications of topological phase transitions and topological phases of matter in honour of this momentous occasion.

Prof. Bachtold’s talk entitled ‘Topological phase transition in liquid helium’ discussed the topological phase transition proposed by Thouless and Kosterlitz for two-dimensional (2-D) liquid helium, first recalling that the transition between superfluid and normal fluid in 3-D is related to symmetry breaking. This is very similar to the phase transition between ice and water. In their seminal work, Thouless and Kosterlitz showed that the transition becomes completely different in 2-D. The phase transition becomes continuous and is related to superfluid vortices. He also presented the experiments of Bishop and Reppy on 2-D liquid helium, which are consistent with a topological phase transition.

Prof. Lewenstein’s talk entitled ‘Physics and Topology’ covered some of Thouless, Kosterlitz and Haldane’s great discoveries. He devoted most of the time to topology in 2D and the Kosterlitz-Thouless-Berezinskii (KBT) transition and discussed two dimensional materials and vortices, as well as the so called, Mermin-Wagner-Hohenberg curse. He offered a short crash course on KTB transitions. In the second part of this talk, he focussed on systems in strong magnetic fields and time reversal (TR) symmetry breaking. Concentrating on the paradigm example of Integer Quantum Hall Effect, he explained the quantization of the conductivity and relation to topological invariants - Chern numbers. Finally, he discussed topological insulators that do not require breaking of the TR symmetry, mentioning Haldane model and spin orbit coupling.