Emergent SU(4) Symmetry and Crystalline Spin-Orbital Liquids
An international team of the Scientists from University of Stuttgart and University of Tokyo has proposed a recipe for the realization of quantum spin-orbital liquids with emergent SU(4) symmetry.
Quantum spin liquids are an exotic state of matter induced by quantum fluctuations. We propose a new mechanism to realize them by increased quantum fluctuations due to an enhanced symmetry, which naturally occurs in a class of materials. In usual magnets, the spin interaction is invariant under spatial rotation, which is mathematically identified with the SU(2) symmetry which mixes two spin states: up and down. It has been suggested that, when an electron can occupy one of two orbitals in an atom, we may realize a larger SU(4) symmetry, which mixes four (2 spin times 2 orbital) states. If such a symmetry enhancement indeed occurs, it is advantageous to destroy long-range order to realize a quantum spin liquid. However, in general, the four states are not equivalent and the SU(4) symmetry cannot be expected. The present work demonstrated theoretically that in a compound α-ZrCl3 the strong spin-orbit coupling, which usually breaks even the original SU(2) symmetry, actually leads to the enhanced SU(4) symmetry. As a consequence, it is predicted as a material realization of quantum spin liquid.
Masahiko G. Yamada, Masaki Oshikawa, and George Jackeli,
Emergent SU(4) Symmetry in α-ZrCl3 and Crystalline Spin-Orbital Liquids,
Phys. Rev. Lett. 121, 097201 (2018).