Spin-Orbital Quantum Liquid on the Honeycomb Lattice
Abstract
The main characteristic of Mott insulators, as compared to band insulators, is to host low-energy spin fluctuations. In addition, Mott insulators often possess orbital degrees of freedom when crystal-field levels are partially filled. While in the majority of Mott insulators, spins and orbitals develop long-range order, the possibility for the ground state to be a quantum liquid opens new perspectives. In this paper, we provide clear evidence that the spin-orbital SU(4) symmetric Kugel-Khomskii model of Mott insulators on the honeycomb lattice is a quantum spin-orbital liquid. The absence of any form of symmetry breaking—lattice or SU(N)—is supported by a combination of semiclassical and numerical approaches: flavor-wave theory, tensor network algorithm, and exact diagonalizations. In addition, all properties revealed by these methods are very accurately accounted for by a projected variational wave function based on the π-flux state of fermions on the honeycomb lattice at 1/4 filling. In that state, correlations are algebraic because of the presence of a Dirac point at the Fermi level, suggesting that the symmetric Kugel-Khomskii model on the honeycomb lattice is an algebraic quantum spin-orbital liquid. This model provides an interesting starting point to understanding the recently discovered spin-orbital-liquid behavior of Ba3CuSb2O9. The present results also suggest the choice of optical lattices with honeycomb geometry in the search for quantum liquids in ultracold four-color fermionic atoms.
- Publication:
-
Physical Review X
- Pub Date:
- October 2012
- DOI:
- 10.1103/PhysRevX.2.041013
- arXiv:
- arXiv:1207.6029
- Bibcode:
- 2012PhRvX...2d1013C
- Keywords:
-
- 75.10.Jm;
- 75.10.Kt;
- 67.85.-d;
- 75.25.Dk;
- Quantized spin models;
- Ultracold gases trapped gases;
- Condensed Matter - Strongly Correlated Electrons;
- Condensed Matter - Quantum Gases
- E-Print:
- 10 pages, 7 figures