Single-band Hubbard model with spin-orbit coupling

Liang Du, Li Yu Huang, Xi Dai

Nitin Kaushal, J. Herbrych, Alberto Nocera +4 more

Giuseppe Guarnaccia, Canio Noce

Using Bogoliubov's inequality we rigorously show that the multiorbital Hubbard model with narrow bands, even in the presence of spin-orbit coupling, does not exhibit long-range nematic order, in low dimensions. This result holds at any finite temperature for both repulsive and attractive Coulomb interactions, with and without spin-orbit coupling.

Markus Aichhorn

T. Herrmann, Wolfgang Nolting

Nitin Kaushal, Alberto Nocera, Gonzalo Álvarez +2 more

Theoretical studies recently predicted the condensation of spin-orbit excitons at momentum $q=\ensuremath{\pi}$ in ${t}_{2g}^{4}$ spin-orbit coupled three-orbital Hubbard models at electronic density $n=4$. In parallel, experiments involving iridates with noninteger valence states for the Ir ions are starting to attract considerable attention. In this publication, using the density matrix renormalization group technique we present evidence for the existence of an excitonic condensate at $n=3.5$ in a one-dimensional Hubbard model with a degenerate ${t}_{2g}$ sector, when in the presence of spin-orbit coupling. At intermediate Hubbard $U$ and spin-orbit $\ensuremath{\lambda}$ couplings, we found an excitonic condensate at the unexpected momentum $q=\ensuremath{\pi}/2$ involving ${j}_{\mathrm{eff}}=3/2,m=\ifmmode\pm\else\textpm\fi{}1/2$, and ${j}_{\mathrm{eff}}=1/2,m=\ifmmode\pm\else\textpm\fi{}1/2$ bands in the triplet channel, coexisting with an also unexpected block magnetic order. We also present the entire $\ensuremath{\lambda}$ vs $U$ phase diagram, at a fixed and robust Hund coupling. Interestingly, this new ``block excitonic phase'' is present even at large values of $\ensuremath{\lambda}$, unlike the $n=4$ excitonic phase discussed before. Our computational study helps to understand and predict the possible magnetic phases of materials with ${d}^{3.5}$ valence and robust spin-orbit coupling.