(searched for: doi:10.1103/physrevb.104.235135)
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.245113
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 with a electronic configuration. Near the Fermi level, in the nonmagnetic phase the dominant states are mainly contributed by the Cu orbitals highly hybridized with the O 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 . 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 is predicted to be negative at Hubbard , suggesting incipient pairing tendencies.
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.104431
In the presence of strong atomic spin-orbit coupling (SOC), tending to the coupling limit, iridates are speculated to possess a nonmagnetic 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, , with well-separated ions. But all the detailed experimental as well as theoretical characterizations reveal that the ground state of is not nonmagnetic. However, our combined dc susceptibility , nuclear magnetic resonance (NMR), muon spin relaxation/rotation , and heat capacity measurements clearly refute any sign of spin freezing or ordered magnetism among the moments due to geometrical exchange frustration, while in-depth zero-field and longitudinal field 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 iridates is unlikely to offer a ground state which will be consistent with a purely atomic coupling description.