Anyonic quantum spin chains: Spin-1 generalizations and topological stability

Abstract

There are many interesting parallels between systems of interacting non-Abelian anyons and quantum magnetism occurring in ordinary SU(2) quantum magnets. Here we consider theories of so-called su(2)${}_{k}$ anyons, well-known deformations of SU(2), in which only the first $k+1$ angular momenta of SU(2) occur. In this paper, we discuss in particular anyonic generalizations of ordinary SU(2) spin chains with an emphasis on anyonic spin $S=1$ chains. We find that the overall phase diagrams for these anyonic spin-1 chains closely mirror the phase diagram of the ordinary bilinear-biquadratic spin-1 chain including anyonic generalizations of the Haldane phase, the AKLT construction, and supersymmetric quantum critical points. A novel feature of the anyonic spin-1 chains is an additional topological symmetry that protects the gapless phases. Distinctions further arise in the form of an even/odd effect in the deformation parameter $k$ when considering su(2)${}_{k}$ anyonic theories with $k\ensuremath{\ge}5$, as well as for the special case of the su(2)${}_{4}$ theory for which the spin-1 representation plays a special role. We also address anyonic generalizations of spin-$\frac{1}{2}$ chains with a focus on the topological protection provided for their gapless ground states. Finally, we put our results into the context of earlier generalizations of SU(2) quantum spin chains, in particular so-called (fused) Temperley-Lieb chains.