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arXiv:2204.01688 · Physical review. B./Physical review. B

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

Ling-Fang Lin, Rahul Soni, Yang Zhang, Shang Gao, Adriana Moreo, Gonzalo Álvarez, Andrew D Christianson, M. B. Stone, Elbio R. Dagotto

Published Jun 10, 2022• 6 citations
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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 ${\mathrm{Na}}_{2}{\mathrm{Cu}}_{2}{\mathrm{TeO}}_{6}$ with a ${d}^{9}$ electronic configuration. Near the Fermi level, in the nonmagnetic phase the dominant states are mainly contributed by the Cu $3{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ 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 ${\mathrm{Na}}_{2}{\mathrm{Cu}}_{2}{\mathrm{TeO}}_{6}$. 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 $\ensuremath{\uparrow}\text{\ensuremath{-}}\ensuremath{\downarrow}\text{\ensuremath{-}}\ensuremath{\downarrow}\text{\ensuremath{-}}\ensuremath{\uparrow}$ 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 $\mathrm{\ensuremath{\Delta}}E$ is predicted to be negative at Hubbard $U\ensuremath{\sim}11\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, suggesting incipient pairing tendencies.

DOI
10.1103/physrevb.105.245113

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Spin-12\frac{1}{2}21​ chains with alternating antiferromagnetic (AF) and ferromagnetic (FM) couplings exhibit quantum entanglement as the integer-spin Haldane chains and might be similarly utilized for quantum computations. Such alternating AF-FM chains have been proposed to be realized in the distorted honeycomb lattice compound Na2Cu2TeO6{\mathrm{Na}}_{2}{\mathrm{Cu}}_{2}{\mathrm{TeO}}_{6}Na2​Cu2​TeO6​, but to confirm this picture a comprehensive understanding of the exchange interactions including terms outside of the idealized model is required. Here, we employ neutron scattering to study the spin dynamics in Na2Cu2TeO6{\mathrm{Na}}_{2}{\mathrm{Cu}}_{2}{\mathrm{TeO}}_{6}Na2​Cu2​TeO6​ and accurately determine the coupling strengths through the random phase approximation and density functional theory approaches. We find the AF and FM intrachain couplings are the dominant terms in the spin Hamiltonian, while the interchain couplings are AF but perturbative. This hierarchy in the coupling strengths and the alternating signs of the intrachain couplings can be understood through their different exchange paths. Our results establish Na2Cu2TeO6{\mathrm{Na}}_{2}{\mathrm{Cu}}_{2}{\mathrm{TeO}}_{6}Na2​Cu2​TeO6​ as a weakly coupled alternating AF-FM chain compound and reveal the robustness of the gapped ground state in alternating chains under weak interchain couplings.
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