BCS-BEC crossover in a $(t_{2g})^4$ Excitonic Magnet
| Title: | BCS-BEC crossover in a $(t_{2g})^4$ Excitonic Magnet |
|---|---|
| Authors: | Kaushal, Nitin, Soni, Rahul, Nocera, Alberto, Alvarez, Gonzalo, Dagotto, Elbio |
| Source: | Phys. Rev. B 101, 245147 (2020) |
| Publication Year: | 2020 |
| Collection: | Condensed Matter |
| Subject Terms: | Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science |
| More Details: | The condensation of spin-orbit-induced excitons in $(t_{2g})^4$ electronic systems is attracting considerable attention. In the large Hubbard U limit, antiferromagnetism was proposed to emerge from the Bose-Einstein Condensation (BEC) of triplons ($J_{\textrm{eff}} = 1$). In this publication, we show that even for the weak and intermediate U regimes, the spin-orbit exciton condensation is possible leading also to staggered magnetic order. The canonical electron-hole excitations (excitons) transform into local triplon excitations at large U , and this BEC strong coupling regime is smoothly connected to the intermediate U excitonic insulator region. We solved the degenerate three-orbital Hubbard model with spin-orbit coupling ($\lambda$) in one-dimensional geometry using the Density Matrix Renormalization Group, while in two-dimensional square clusters we use the Hartree-Fock approximation (HFA). Employing these techniques, we provide the full $\lambda$ vs U phase diagrams for both one- and two- dimensional lattices. Our main result is that at the intermediate Hubbard U region of our focus, increasing $\lambda$ at fixed U the system transitions from an incommensurate spin-density-wave metal to a Bardeen-Cooper-Schrieffer (BCS) excitonic insulator, with coherence length r coh of O(a) and O(10a) in 1d and 2d, respectively, with a the lattice spacing. Further increasing $\lambda$, the system eventually crosses over to the BEC limit (with r coh << a). |
| Document Type: | Working Paper |
| DOI: | 10.1103/PhysRevB.101.245147 |
| Access URL: | http://arxiv.org/abs/2002.07351 |
| Accession Number: | edsarx.2002.07351 |
| Database: | arXiv |
Be the first to leave a comment!