$\pi$-Flux Tuning of Quantum Paramagnetism in the Triangular-Lattice Hubbard Model

Abstract

We compare two time-reversal-symmetric triangular-lattice Hubbard models at half filling: the zero-flux model and a staggered $\pi$-flux model with zero and $\pi$ flux through oppositely oriented triangles. Although both reduce to the same Heisenberg model at leading order in the strong-coupling limit, their distinct charge fluctuation profiles yield different quantum paramagnetic regimes. Combining a strong-coupling expansion with infinite density matrix renormalization group (iDMRG) calculations, we find that the positive ring-exchange of the zero-flux model promotes spontaneous chirality, consistent with its notion of a chiral spin liquid at intermediate coupling. In the staggered-$\pi$-flux model, whose noninteracting limit is a Dirac semimetal, the ring exchange changes sign and disfavors chiral order and we find no resolvable scalar chirality. This renders flux-tuned ring-exchange an efficient discriminator between chiral and non-chiral quantum paramagnets at finite coupling.

arXiv comment5 pages, 5 figures, plus Supplemental Material