Magnetization dynamics fingerprints of an excitonic condensate $t_{2g}^4$ magnet

Journal Article · Mon Dec 20 00:00:00 UTC 2021 · Physical Review B

DOI: https://doi.org/10.1103/physrevb.104.235135 · OSTI ID:1838948

Kaushal, Nitin ^[1]; Herbrych, Jacek ^[2]; Alvarez, Gonzalo  ^[3]; Dagotto, Elbio R. ^[4]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. Wroclaw Univ. of Science and Technology (Poland)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)

The competition between spin-orbit coupling (SOC) $\lambda$ and electron-electron interaction $U$ leads to a plethora of novel states of matter, extensively studied in the context of $t_{2g}^4$ and $t_{2g}^5$ materials, such as ruthenates and iridates. Excitonic magnets—the antiferromagnetic state of bounded electron-hole pairs-are prominent examples of phenomena driven by those competing energy scales. Interestingly, recent theoretical studies predicted that excitonic magnets can be found in the ground state of SOC $t_{2g}^4$ Hubbard models. Here we present a detailed computational study of the magnetic excitations in that excitonic magnet, employing one-dimensional chains (via density matrix renormalization group) and small two-dimensional clusters (via Lanczos). Specifically, first we show that the low-energy spectrum is dominated by a dispersive (acoustic) magnonic mode, with extra features arising from the $\lambda =0$ state in the phase diagram. Second, and more importantly, we found a novel magnetic excitation forming a high-energy optical mode with the highest intensity at wave-vector $q\to 0$. In the excitonic condensation regime at large $U$, we also have found a novel high-energy $\pi$ mode composed solely of orbital excitations. Overall, these features do not appear all together in any of the neighboring states in the phase diagram and thus constitute unique fingerprints of the $t_{2g}^4$ excitonic magnet, of importance in the analysis of neutron and resonant inelastic x-ray scattering experiments.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: National Science Centre Poland (NCN); Polish National Agency for Academic Exchange (NAWA); USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1838948
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 23 Vol. 104; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English