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Anomalous Self-Energy Features in the 2D Hubbard Model

100%
Avella A., Mancini F.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
395-398
EN
The electronic self-energy of the two-dimensional Hubbard model, computed in the non-crossing approximation within the composite operator method, is studied as a function of frequency as well as temperature at the Fermi surface, for a value of doping at which the pseudogap is already well developed. For values of momentum belonging to the phantom arc of the Fermi surface, both dependences show anomalous power law behavior in contrast to that expected from the Fermi liquid theory.
2
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Study of the Mott Transition in the Three-Dimensional Hubbard Model

100%
Mancini F., Turkowski V.
Acta Physica Polonica A
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2002
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vol. 101
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issue 4
505-523
EN
The Mott-Hubbard transition in the three-dimensional Hubbard model is studied by means of the composite operator method. Analytical and numerical calculations show the existence of a critical value U_c of the Coulomb interaction which separates paramagnetic insulating and metallic phases. In the composite operator method the ratio U_c/W, where W is the band width, has the same value as in the two-dimensional case. The ground state of the Mott insulator is characterized by a local antiferromagnetic order where the electrons keep some mobility, but this latter must be compatible with the local ordering. By analyzing the intersite hopping it is possible to establish that some correlation functions behave as order parameters in the insulating phase.
3
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Frustration-Driven Quantum Phase Transition in the 1D Extended Anisotropic Heisenberg Model

81%
Plekhanov E., Avella A., Mancini F.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
429-432
EN
By using density matrix renormalization group technique we study the 1D extended anisotropic Heisenberg model. We find that starting from the ferromagnetic phase, the system undergoes two quantum phase transitions induced by frustration. By increasing the next-nearest-neighbor interaction, the ground state of the system changes smoothly from a completely polarized state to a next-nearest-neighbor correlated one. On the contrary, letting the in-plane interaction to be greater than the out-of-plane one, the ground state changes abruptly.
4
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Entanglement Properties and Phase Diagram of the Two-Orbital Atomic Hubbard Model

81%
Avella A., Mancini F., Scelza G., Chaturvedi S.
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EN
We study the two-orbital Hubbard model in the limit of vanishing kinetic energy. The phase diagram in the V-J plane, with V and J denoting the interorbital hybridization and exchange coupling respectively, at half filling is obtained. A singlet(dimer)-triplet transition is found for a critical value of the ratio V/J. The entropy of formation, both in the mode and in the particle pictures, presents a jump at the same critical line in conformity with the suggested relation between criticality and entanglement.
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