In: Journal of Superconductivity and Novel Magnetism, 2011, vol. 24, no. 3, p. 1157-1159
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In: Journal of Superconductivity and Novel Magnetism, 2011, vol. 24, no. 3, p. 1157-1159
The two-dimensional repulsive Hubbard model has been investigated by a variety of methods, from small to large U. Superconductivity with d-wave symmetry is consistently found close to half filling. After a brief review of the various methods a variational many-electron state is discussed in more detail. This trial state is a natural extension of the Gutzwiller ansatz and provides a...
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In: Physical Review B, 2009, vol. 79, no. 8, p. 085121
We investigated excitation spectra of the one-dimensional chain compound Sr₂CuO₃. The small peak at 2.3 eV in the loss function turned out to correspond to the strong charge-transfer transition at 1.8 eV in conductivity. It has the excitonic character expected in one-dimensional extended Hubbard model of the transition from the lower Hubbard band to the Zhang-Rice singlet state. The strongest...
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In: Physical Review B, 2009, vol. 79, no. 16, p. 165109
We investigate the neutral-to-ionic insulator-insulator transition in one-dimensional materials by treating a strong-coupling effective model based on the ionic Hubbard model using the density-matrix renormalization group and finite-size scaling. The effective model, formulated in a spin-one representation, contains a single parameter. We carry out an extensive finite-size scaling analysis of the...
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In: Physical Review B, 2009, vol. 79, no. 10, p. 100510(R)
An elaborate variational wave function is used for studying superconductivity in the (repulsive) two-dimensional Hubbard model, including both nearest- and next-nearest-neighbor hoppings. A marked asymmetry is found between the “localized” hole-doped region and the more itinerant electron-doped region. Superconductivity with d-wave symmetry turns out to be restricted to densities where...
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