Zernike Chair Colloquium 2017 - Jeroen van den Brink: Anyone seen an anyon?

Particles in our three-dimensional world must be either bosons or fermions: exchanging two identical particles either leaves the quantum mechanical wavefunction invariant (bosons) or causes a sign-change (fermions). Consequently, elementary particles obey either Bose–Einstein or Fermi-Dirac statistics.

Quantum mechanics in a world with only two space dimensions (2D) is much richer. In principle particles can exist in 2D that are "in between" bosons and fermions. Such particles, anyons, are predicted to they have very peculiar physical properties. First of all, exchanging two identical anyons produces a change of the phase of the wavefunction that is anywhere between 0 and π. Second, moving two anyons around each other in the 2D plane can even change the identity of the anyons. The latter property renders anyons essential building blocks for a future topological quantum computer.

In the Colloquium I will introduce and discuss a number of real materials in which anyons might be observable, in particular quasi-2D honeycomb iridates and ruthenates. It will become clear that these strongly correlated magnetic materials are candidates to host a topological spin-liquid state that was predicted by A. Kitaev in 2006. There is strong experimental and theoretical evidence that in one of these materials, α-ruthenium trichloride, fractionalized quasiparticles are present, but has anyone seen an anyon?