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Electronic structure, magnetic properties, and pairing tendencies of the copper-based honeycomb lattice Na2Cu2TeO6...

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Physical Review B
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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 3dx2−y2 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 U∼11eV, suggesting incipient pairing tendencies.