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(searched for: doi:10.1103/physrevb.104.235135)
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Ling-Fang Lin, Rahul Soni, , Shang Gao, Adriana Moreo, Gonzalo Alvarez, Andrew D. Christianson, , Elbio Dagotto
Published: 10 June 2022
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.245113

Abstract:
Spin-1/2 chains with alternating antiferromagnetic (AFM) and ferromagnetic (FM) couplings have attracted considerable interest due to the topological character of their spin excitations. Here, using density functional theory and density-matrix renormalization-group (DMRG) methods, we have systematically studied the dimerized chain system Na2Cu2TeO6 with a d9 electronic configuration. Near the Fermi level, in the nonmagnetic phase the dominant states are mainly contributed by the Cu 3dx2y2 orbitals highly hybridized with the O 2p orbitals, leading to an “effective” single-orbital low-energy model. By calculating the relevant hoping amplitudes, we explain the size and sign of the exchange interactions in Na2Cu2TeO6. In addition, a single-orbital Hubbard model is constructed for this dimerized chain system where the quantum fluctuations are taken into account. Both AFM and FM couplings (leading to an state) along the chain were found in our DMRG and Lanczos calculations, in agreement with density functional theory and neutron-scattering results. The hole pairing binding energy ΔE is predicted to be negative at Hubbard U11eV, suggesting incipient pairing tendencies.
Abhisek Bandyopadhyay, , , Vinod Kumar, , A. Efimenko, F. Bert, , C. Meneghini, N. Büttgen, et al.
Published: 28 March 2022
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.104431

Abstract:
In the presence of strong atomic spin-orbit coupling (SOC), tending to the jj coupling limit, 5d4 iridates are speculated to possess a nonmagnetic Jeff=0 singlet ground state from atomic consideration, which invariably gets masked due to different solid-state effects (e.g., hopping). Here, we try to probe the trueness of the atomic SOC-based proposal in an apparently one-dimensional system, Sr3NaIrO6, with well-separated Ir5+(5d4) ions. But all the detailed experimental as well as theoretical characterizations reveal that the ground state of Sr3NaIrO6 is not nonmagnetic. However, our combined dc susceptibility χ, Na23 nuclear magnetic resonance (NMR), muon spin relaxation/rotation (μSR), and heat capacity Cp measurements clearly refute any sign of spin freezing or ordered magnetism among the Ir5+ moments due to geometrical exchange frustration, while in-depth zero-field and longitudinal field μSR investigations strongly point towards an inhomogeneous quantum spin liquid (QSL)-like ground state. In addition, the linear temperature dependence of both the NMR spin-lattice relaxation rate and the magnetic heat capacity at low temperatures suggest low-lying gapless spin excitations in the QSL phase of this material. Finally, we conclude that the effective SOC realized in d4 iridates is unlikely to offer a ground state which will be consistent with a purely atomic jj coupling description.
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