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(searched for: doi:10.1103/physrevb.104.l060102)
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, Ling-Fang Lin, Adriana Moreo, Elbio Dagotto
Published: 10 January 2022
Applied Physics Letters, Volume 120; https://doi.org/10.1063/5.0079570

Abstract:
Using ab initio density functional theory, we study the electronic and magnetic properties of the van der Waals chain material OsCl4. In the nonmagnetic state, a strongly anisotropic band structure was observed, in agreement with its anticipated one-dimensional crystal geometry. Based on Wannier functions, we found that the four electrons of the 5d Os atom form a low-spin S = 1 state, with a large crystal field between the dxz/yz and dxy orbitals, corresponding to a strong Jahn–Teller distortion (Q3<0 ). As a consequence, the magnetic properties are mainly contributed by the dxz/yz states. Furthermore, when a Mott gap develops after the introduction of the Hubbard U and Hund coupling J, we found that the staggered spin order is the most likely magnetic state, namely, spins arranged as (↑-↓-↑-↓) with π wavevector along the chain. In addition, the energy differences between various spin states are small, suggesting a weak magnetic exchange coupling along the chain. Our results provide guidance to experimentalists and theorists working on quasi-one-dimensional osmium halides chain materials.
, Jacek Herbrych, Gonzalo Alvarez, Elbio Dagotto
Published: 20 December 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.235135

Abstract:
The competition between spin-orbit coupling (SOC) λ and electron-electron interaction U leads to a plethora of novel states of matter, extensively studied in the context of t2g4 and t2g5 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 t2g4 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 λ=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 q0. In the excitonic condensation regime at large U, we also have found a novel high-energy π mode composed solely of orbital excitations. These features do not appear all together in any of the neighboring states in the phase diagram and thus constitute unique fingerprints of the t2g4 excitonic magnet, of importance in the analysis of neutron and resonant inelastic x-ray scattering experiments.
, Ling-Fang Lin, Gonzalo Alvarez, Adriana Moreo, Elbio Dagotto
Published: 15 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.125122

Abstract:
Quasi-one-dimensional iron-based ladders and chains, with the 3d iron electronic density n=6, are attracting considerable attention. Recently, a new iron chain system Ba2FeS3, also with n=6, was prepared under high-pressure and high-temperature conditions. Here the magnetic and electronic phase diagrams are theoretically studied for this quasi-one-dimensional compound. Based on first-principles calculations, a strongly anisotropic one-dimensional electronic band behavior near the Fermi level was observed. In addition, a three-orbital electronic Hubbard model for this chain was constructed. Introducing the Hubbard and Hund couplings and studying the model via the density matrix renormalization group (DMRG) method, we studied the ground-state phase diagram. A robust staggered AFM region was unveiled in the chain direction, consistent with our density functional theory (DFT) calculations. Furthermore, at intermediate Hubbard U coupling strengths, this system was found to display an orbital selective Mott phase (OSMP) with one localized orbital and two itinerant metallic orbitals. At very large U/W(W=bandwidth), the system displays Mott insulator characteristics, with two orbitals half-filled and one doubly occupied. Our results for high pressure Ba2FeS3 provide guidance to experimentalists and theorists working on this one-dimensional iron chalcogenide chain material.
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