Dipolar-Octupolar Doublets and Theory of Quantum Kagome Ice
Yi-Ping Huang1,2*, Michael Hermele2
1Condensed matter physics, the Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
2Physics, University of Colorado Boulder, Boulder, USA
* Presenter:Yi-Ping Huang, email:yihu@pks.mpg.de
How novel topological quantum states emerge from realistic systems is a challenging problem. Furthermore, the numerical and experimental signature to identify the topological nature of the novel quantum states is the key information to connect to material realizations. We derive an effective Z2 gauge theory to describe the quantum kagome ice (QKI) state that has been observed by Carrasquilla et al. [Nat. Commun. 6, 7421 (2015)] in Monte Carlo studies of the S=1/2 kagome XYZ model in a Zeeman field. The numerical results on QKI are consistent with, but do not confirm or rule out, the hypothesis that it is a Z2 spin liquid. Our effective theory allows us to explore this hypothesis and make a striking prediction for future numerical studies, namely, that symmetry-protected vison zero modes arise at lattice disclination defects, leading to a Curie defect term in the spin susceptibility, and a characteristic (Ndis−1)ln2 contribution to the entropy, where Ndis is the number of disclinations. Only the Z2 Ising symmetry is required to protect the vison zero modes. This is remarkable because a unitary Z2 symmetry cannot be responsible for symmetry-protected degeneracies of local degrees of freedom. We also discuss other signatures of symmetry fractionalization in the Z2 spin liquid, and phase transitions out of the Z2 spin liquid to nearby ordered phases.

Keywords: Topological order, Quantum spin liquid, Strong spin-orbit coupled materials, Frustrated magnetism