Download Article PDF

Feature Articles


Early experimental evidence of a topological quantum state: The signature of the Haldane ground state revealed by scattered neutrons


Mechthild Enderle - Institut Laue-Langevin
Michel Kenzelmann - Paul-Scherrer Institut
W.J.L. (Bill) Buyers - Canadian Neutron Beam Centre


The experimental confirmation of the Haldane gap in 1985 by researchers working at Chalk River was a major contribution toward validating the theoretical ideas of Thouless, Haldane, and Kosterlitz, who won the Nobel Prize in Physics in 2016. This article reviews the signatures of Haldaneā€™s predicted topological quantum ground state and their observation in early neutron scattering experiments, which overturned the wisdom of the day.