We analyze a diamond chain containing itinerant electrons interacting via local on-site Coulomb interaction by a method based on positive semidefinite operators. The constant external magnetic field is taken into account by Peierls phase factor terms in the kinetic energy part of the Hamiltonian. We deduced exact ground states containing linear and bilinear combinations of fermionic creation operators acting on the vacuum state for arbitrary strong Hubbard repulsion. Physically, the linear solutions can be non-magnetic and ferromagnetic, while the bilinear solutions, which mean electron-pairs, can only be non-magnetic.
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For E.K. (Z.G.), this work was carried out as part of the TAMOP-4.2.1.B-10/2/KONV-2010-0001, (TAMOP-4.2.1/B-09/1/KONV-2010-0007) project in the framework of the New Hungarian Development Plan and for Z.G. also OTKA-K-100288.
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Kovács, E., Gulácsi, Z. Electron Pairs in the Ground States of Chain Structures. J Supercond Nov Magn 26, 1781–1785 (2013). https://doi.org/10.1007/s10948-012-2028-9