In order to provide a numerical criterion for superconductivity, the ground state energy ${\mathit{E}}_{0}$ (\ensuremath{\Phi}) is calculated for the attractive and repulsive Hubbard models on a cylinder geometry threaded by a flux \ensuremath{\Phi}. From the functional form of ${\mathit{E}}_{0}$ (\ensuremath{\Phi}), superconducting ground states may be identified without prior knowledge of the pairing symmetry. ${\mathit{E}}_{0}$ (\ensuremath{\Phi}) is calculated with Monte Carlo methods. For the attractive Hubbard model, our results confirm the existence of a superconducting ground state. In contrast, our results show that the quarter-filled repulsive Hubbard model is not superconducting and that a Hartree-Fock paramagnetic approximation fits the data very well.In order to provide a numerical criterion for superconductivity, the ground state energy ${\mathit{E}}_{0}$(\ensuremath{\Phi}) is calculated for the attractive and repulsive Hubbard models on a cylinder geometry threaded by a flux \ensuremath{\Phi}. From the functional form of ${\mathit{E}}_{0}$(\ensuremath{\Phi}), superconducting ground states may be identified without prior knowledge of the pairing symmetry. ${\mathit{E}}_{0}$(\ensuremath{\Phi}) is calculated with Monte Carlo methods. For the attractive Hubbard model, our results confirm the existence of a superconducting ground state. In contrast, our results show that the quarter-filled repulsive Hubbard model is not superconducting and that a Hartree-Fock paramagnetic approximation fits the data very well.

Physical Review LettersSep 20, 199335 citations

Variational tests of current order parameters in the Hubbard model

Alexander A. Ovchinnikov, M. Ya. Ovchinnikova

Variational tests are performed for current order parameters as probable sources of the pseudogap normal state of cuprates. The calculations are carried out based on the states with correlations of the valence bond type whose formation can induce in principle both the superconducting order of the d symmetry and current phases. It is shown for the t-t′ -U Hubbard models with a large value of U (∼8 t ) and the Hubbard splitting of the conduction band that (1) phases of alternating charge and longitudinal spin currents cannot be realized and (2) transverse spin currents are not compatible with the superconducting order and they could exist against the normal-state background only within a very narrow doping region near the optimal one. This region does not correspond to the region of existence of a pseudogap in cuprates, which refutes the above-mentioned hypothesis of the pseudogap origin. The requirements to the parameters of models for which the consideration of correlations of the valence bond type yields a reasonable phase curve. The existence of current phases in the t-t′-U-V Hubbard models with a strong interaction ( V >0.25t) of particles in neighboring sites is predicted when the d -superconductivity is completely suppressed.Variational tests are performed for current order parameters as probable sources of the pseudogap normal state of cuprates. The calculations are carried out based on the states with correlations of the valence bond type whose formation can induce in principle both the superconducting order of the d symmetry and current phases. It is shown for the t-t′ -U Hubbard models with a large value of U (∼8 t ) and the Hubbard splitting of the conduction band that (1) phases of alternating charge and longitudinal spin currents cannot be realized and (2) transverse spin currents are not compatible with the superconducting order and they could exist against the normal-state background only within a very narrow doping region near the optimal one. This region does not correspond to the region of existence of a pseudogap in cuprates, which refutes the above-mentioned hypothesis of the pseudogap origin. The requirements to the parameters of models for which the consideration of correlations of the valence bond type yields a reasonable phase curve. The existence of current phases in the t-t′-U-V Hubbard models with a strong interaction ( V >0.25t) of particles in neighboring sites is predicted when the d -superconductivity is completely suppressed.

Journal of Experimental and Theoretical PhysicsJul 1, 20010 citations

On the theory of superconductivity in the extended Hubbard model

Nikolay M. Plakida, V. S. Oudovenko

The European Physical Journal BMar 1, 201338 citations

Superconductivity within the extended Hubbard model

Rene Jursa, S. Wermbter, G. Czycholl

Czechoslovak Journal of PhysicsFeb 1, 19962 citations

On the Theory of Superconductivity in the Extended Hubbard Model

Julia Mihailowa Wesselinowa

physica status solidi (b)Dec 1, 19890 citations

In order to provide a numerical criterion for superconductivity, the ground state energy

{\mathit{E}}_{0}

(\ensuremath{\Phi}) is calculated for the attractive and repulsive Hubbard models on a cylinder geometry threaded by a flux \ensuremath{\Phi}. From the functional form of

{\mathit{E}}_{0}

(\ensuremath{\Phi}), superconducting ground states may be identified without prior knowledge of the pairing symmetry.

{\mathit{E}}_{0}

(\ensuremath{\Phi}) is calculated with Monte Carlo methods. For the attractive Hubbard model, our results confirm the existence of a superconducting ground state. In contrast, our results show that the quarter-filled repulsive Hubbard model is not superconducting and that a Hartree-Fock paramagnetic approximation fits the data very well.