Quantum spin fluid

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A state of matter is called quantum spin fluid that does not have any aligned quantum spins even at the lowest temperatures .

In a typical magnetic material, the spins of the electrons all align in the same way at low temperatures . In contrast, in a quantum spin fluid, the electrons remain an entangled ensemble even at absolute zero, which shows quantum fluctuations .

According to a theoretical model, so-called Majorana fermions can arise in such a quantum spin fluid . These are quasiparticles with half-integer spin that are also their own antiparticles . So far it has hardly been possible to grasp them, although they were postulated as early as 1937. In a two-dimensional material researchers were able to Arnab Banerjee from the Oak Ridge National Laboratory by neutron scattering experiments in 2015 Majorana fermions (and thus the existence of a quantum spin liquid) experimentally demonstrated. They use α- ruthenium (III) chloride as a material that has a layered structure similar to graphene . The researchers were able to confirm computer simulations from 2014.

In the meantime, different quantum spin fluids are known, which can be roughly divided into two classes: Spin fluids whose elementary excitations, the so-called spinons , remain massless. The energy spectrum of these type I spin fluids therefore has no excitation gap above the quantum mechanical ground state and often shows a linear energy dispersion . The second large class of spin fluids has an excitation gap to massive quasiparticles in the energy spectrum. The distinctive property of these type II spin fluids is the development of a non-local, topological order , which is why these phases are entangled over a long range despite the finite correlation length.

Individual evidence

  1. ↑ a b Philipp Hummel: Quantum Physics: Quantum spin fluid does not want to be organized. In: Spectrum of Science. accessed on June 2, 2016.
  2. ↑ A. Banerjee, CA Bridges, J.-Q. Yan, AA Aczel, L. Li, MB Stone, GE Granroth, MD Lumsden, Y. Yiu, J. Knolle, S. Bhattacharjee, DL Kovrizhin, R. Moessner, DA Tennant, DG Mandrus, SE Nagler: Proximate Kitaev quantum spin liquid behavior in a honeycomb magnet. In: Nature Materials. 2016, doi: 10.1038 / nmat4604 .
  3. ↑ Kai Phillip Schmidt, Simon Trebst: Topological spin liquids In: Physik Journal . 04/2015, p. 39.