Spin-orbital-entangled quantum magnet on a honeycomb lattice

H. Takagi

Kentaro Kitagawa, T. Takayama, Y. Matsumoto +7 more

P. Gegenwart

Spin-Orbital Entangled Quantum Liquid on Honeycomb Lattice Authors: K. Kitagawa, T. Takayama, Y. Matsumoto, A. Kato, R. Takano , Y. Kishimoto, S. Bette, R. Dinnebie, G. Jackeli, and H. Takagi H. Takagi, KITP talk, Aug 2017 Recommended with a commentary by Patrick A. Lee and T. Senthil, Massachusetts Institute of Technology. |View Commentary| DOI: 10.36471/JCCM_November_2017_02 […]

Masahiko G. Yamada

We perform large-scale density matrix renormalization group simulations of the SU(4) Heisenberg model on the honeycomb lattice to address the long-standing question of its ground state in an unbiased and quantitatively controlled manner. We find reliable numerical evidence that the ground state is a gapped spin-orbital liquid, presumably with a Z_{4} topological order, characterized by a finite topological entanglement entropy close to ln(4), the absence of both SU(4) and lattice symmetry breaking, and a variationally optimized ground-state energy well below the previously proposed π-flux variational state. By exploiting full SU(4) symmetry and keeping up to 12 800 SU(4) multiplets, corresponding to more than 1×10^{6} U(1) states, we achieve unprecedented accuracy for two-dimensional SU(4) quantum magnets. Finite-size scaling of energies and entanglement entropies supports a robust gapped phase in the two-dimensional limit, while a gapless critical state on narrow cylinders is identified as a proximate remnant of a Dirac spin-orbital liquid. Our results find the SU(4) honeycomb Heisenberg model a realization of a gapped topological spin-orbital liquid and provide convincing numerical evidence for topological order in a highly symmetric two-dimensional quantum magnet.

Masahiko G. Yamada, Masaki Oshikawa, George Jackeli

An emergent SU(4) symmetry discovered in the microscopic model for d1 honeycomb materials [M. G. Yamada, M. Oshikawa, and G. Jackeli, ] has enabled us to tailor exotic SU(4) models in real materials. In the honeycomb structure, the emergent SU(4) Heisenberg model would potentially have a quantum spin-orbital liquid ground state due to the , and we can also expect similar spin-orbital liquids in three-dimensional versions of the honeycomb lattice. In such quantum spin-orbital liquids, both the spin and orbital degrees of freedom become fractionalized and entangled together due to the strong frustrated interactions between them. Similarly to spinons in pure quantum spin liquids, quantum spin-orbital liquids can host not only spinon excitations, but also fermionic excitations at low temperature.