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

Ling-Fang Lin, Rahul Soni, Shang Gao, Adriana Moreo, Gonzalo Alvarez, Andrew D. Christianson, Elbio Dagotto
Published: 10 June 2022

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 $3{d}_{{x}^{2}-{y}^{2}}$ 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 $↑\text{−}↓\text{−}↓\text{−}↑$ 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 $\mathrm{\Delta }E$ is predicted to be negative at Hubbard $U\sim 11\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, suggesting incipient pairing tendencies.
Keywords: functional / http / xmlns / www.w3.org/1998/Math/MathML / mrow / msub / DMRG

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