[Seminar] "Quantum Spin Liquids Coupled to Other Degrees of Freedom" Mr. Masahiko G. Yamada

Abstract:
In the last decades, we observed discovery of various new quantum spin liquids ranging from organic triangular materials to Kitaev-type spin-orbit coupled materials. However, theorists often regard such materials as pure spin systems ignoring the coupling between spins and other dynamical degrees of freedom. We newly focus on the coexisting fluctuations of spin degrees of freedom and other internal degrees of freedom in real materials, such as an orbital fluctuation, a lattice degree of freedom, and charge inhomogeneity.

Quantum spin-orbital liquids are quantum spin liquids coupled to unfrozen orbital degeneracy, theoretically predicted in the SU(4) Heisenberg model on the honeycomb lattice. We newly propose α-ZrCl3 as a new candidate for such a model, and the first candidate for a quantum spin liquid + orbital liquid [1].
We also discuss the possibility of crystalline spin liquids, where crystalline symmetries of the lattice plays a critical role in the protection of the spin liquid state [1,2].
Finally, we propose a new exactly solvable model, where a quantum spin liquid or resonating valence bond state coexists with a quantum proton motion, which we name quantum valence bond ice. We can regard this systems as a new quantum spin- dipole liquid, where quantum spin fluctuations are purely coming from the coupling to the quantum proton motion, and a possible relation to a material called κ-H3(Cat-EDT-TTF)2 will be discussed [3].

[1] M. G. Yamada, M. Oshikawa and G. Jackeli, arXiv:1709.05252.
[2] M. G. Yamada, V. Dwivedi and M. Hermanns,
      Phys. Rev. B 96, 155107 (2017).
[3] M. G. Yamada and Y. Tada, in preparation.