Masahiko Yamada

---

A promising approach to realize quantum spin liquids is to enhance
the spin-space symmetry from usual SU(2) to SU(N). While the SU(N)
symmetry with a general N is proposed in ultracold atoms using
nuclear spin degrees of freedom, its realization in magnetic
materials is challenging. Here we propose a new mechanism by
which the SU(4) symmetry emerges in the strong spin-orbit coupling
limit. The spin-orbit coupling in d^1 transition metal compounds
with edge-sharing anion octahedra leads to strongly
bond-dependent hopping, which is apparently not SU(4)-symmetric.
However, in the honeycomb structure, a gauge transformation maps
the system to an SU(4)-symmetric Hubbard model. In the strong
repulsion limit at quarter filling, the low-energy effective model
is the SU(4) Heisenberg model on the honeycomb lattice, which
cannot have a trivial gapped ground state and is expected to
host a gapless spin-orbital liquid. By generalizing this model
to other three-dimensional lattices, we also propose crystalline
spin-orbital liquids protected by this emergent SU(4) symmetry
and space group symmetries.

---

ISSP, University of Tokyo
Seminar Room 0.03, ETP
Contact: Simon Trebst