Triangular lattice SU(4) antiferromagnets

We study ground states of SU(4) quantum antiferromagnets on the triangular lattice that arise from Mott-insulating phases of fermions with four flavors. We consider different fillings of the SU(4) fermions, which lead to different representations of SU(4) on each site.

For the case of a single fermion per site, corresponding to the fundamental representation of SU(4), we carry out a variational Monte Carlo (VMC) study uncovering a novel candidate for the ground state of the system. This state features simultaneous breaking of SU(4) flavor symmetry down to SU(3)×U(1) along with bond trimerization. We illuminate our findings by considering a mapping to an effective model of SU(4) spins on the honeycomb lattice with a fundamental - anti-fundamental representation on the two sublattices. We show that the SU(4)-broken state on the triangular lattice maps to a flavor-antiflavor Néel ordering on the honeycomb lattice.

In the case of two fermions per site, which corresponds to the self-conjugate representation of SU(4), we study the bilinear-biquadratic antiferromagnetic model. Considering an effective dimer model, we show that for a finite range of biquadratic couplings the system resides in the RVB spin liquid phase.