An international team of researchers has built quantum spin chains from carbon and provided experimental evidence for the Haldanae phase - one of the most important models of quantum magnetism. The development was achieved under the leadership of Empa and the International Iberian Nanotechnology Laboratory. Using scanning tunneling microscopy, the team provided experimental evidence for the Haldane phase, first predicted in 1983 by F.D.M. Haldane, one of the three winners of the 2016 Nobel Prize in Physics.
Specifically, Haldane predicted that a chain of spin-1 building blocks should be "fractionated" so that the last units behave like spin-½ objects. Using a combination of organic chemistry and surface chemistry in an ultra-high vacuum, one-dimensional spin chains of carbon were fabricated from triangulene, a hydrocarbon molecule with spin 1. The investigation of their magnetic excitations on a gold surface showed that the outermost chain links of the triangulene chains exhibited so-called Kondo resonances, a characteristic spectroscopic fingerprint of spin-½ quantum objects in contact with a metal surface.
Schematic representation of a triangulene quantum spin chain examined on a gold surface with the sharp tip of a scanning tunneling microscope. Each triangulene unit has a total spin of 1, but quantum correlations in the chain lead to spin fractionalization so that the terminal triangulenes have a spin of ½. Image: Empa
In addition to researching linear spin chains, the scientists are also focusing on two-dimensional networks of quantum magnets, promising material platforms for quantum computing.
