11 documents found, page 1 of 2
Superconductivity in the SU(N) Anderson lattice at U = infinity
Araújo, Miguel; Peres, Nuno; Sacramento, Pedro; Vieira, VítorWe present a mean-field study of superconductivity in a generalized N-channel cubic Anderson lattice at U=infinity taking into account the effect of a nearest-neighbor attraction J. The condition U=infinity; is implemented within the slave-boson formalism considering the slave bosons to be condensed. We consider the f-level occupancy ranging from the mixed valence regime to the Kondo limit and study the depende...
Specific heat of the periodic Anderson model: From weak to strong coupling
Peres, Nuno; Sacramento, Pedro; Araújo, MiguelWe study the temperature dependence of the specific heat in the periodic Anderson model as function of the on-site Coulomb interaction, hybridization, and position of the f electrons energy level. At strong coupling (U = infinity) we use slave bosons, whereas at weak coupling we use a simple Hartree-Fock decomposition. We find that both in the strong and weak coupling limits the specific heat of the system pres...
Magnetic and superconducting instabilities in the periodic Anderson model: a ra...
Peres, Nuno; Araújo, MiguelWe study the magnetic and superconducting instabilities of the periodic Anderson model with infinite Coulomb repulsion U in the random-phase approximation. The Neel temperature and the superconducting critical temperature are obtained as functions of electronic density (chemical pressure) and hybridization V (pressure). It is found that close to the region where the system exhibits magnetic order the critical t...
Local-moment formation in the periodic Anderson model with superconducting corr...
Araujo, Miguel; Peres, Nuno; Sacramento, PedroWe study local-moment formation in the presence of superconducting correlations among the f electrons in the periodic Anderson model. Local moments form if the Coulomb interaction U > U-cr. We find that U-cr is considerable stronger in the presence of superconducting correlations than in the nonsuperconducting system. Our studs is done for various values of the f-level energy and electronic density. The smalles...
First-order Generalized Beam Theory for Curved Members with Circular Axis
Peres, Nuno; Gonçalves, Rodrigo; Camotim, DinarThis paper presents a first-order Generalized Beam Theory (GBT) formulation for thin-walled members with circular axis and undergoing complex global-distortional-local deformation. The fundamental equations are derived on the basis of the usual GBT kinematic assumptions (Kirchhoff, Vlasov and wall in-plane inextensibility), leading to a formulation able to retrieve accurate solutions with only a few cross-secti...
Phase diagram and magnetic collective excitations of the Hubbard model for grap...
Peres, Nuno; Araújo, MiguelWe discuss the magnetic phases of the Hubbard model for the honeycomb lattice both in two and three spatial dimensions. A ground state phase diagram is obtained depending on the interaction strength U and electronic density n. We find a first order phase transition between ferromagnetic regions where the spin is maximally polarized (Nagaoka ferromagnetism) and regions with smaller magnetization (weak ferromagne...
Spin waves and renormalized magnetization in single and weakly coupled honeycom...
Araújo, Miguel; Peres, NunoWe discuss the magnetic properties of the Hubbard model in honeycomb lattice layers. A ground state magnetic phase diagram is obtained as a function of interaction, U, and electron density, n. We also calculate the spin wave excitations in the antiferromagnetic insulating phase of single- and double-layered systems within Hartree–Fock-RPA theory. We also study the spin fluctuation correction to the mean field m...
Magnetic excitations in the periodic Anderson model
Sampaio, Maria; Peres, Nuno; Araújo, MiguelA study of spin waves in the magnetic phases of the periodic Anderson modelfor a cubic lattice is carried out in the random-phase approximation. Within mean field theory, we determine the ferromagnetic region of the phase diagram at T ¼ 0: The spin wave spectrum is computed along high symmetry directions of the Brillouin zone. An analytical expression for the spin wave dispersion valid in the small momentum lim...
Weak ferromagnetism and spiral spin structures in honeycomb Hubbard planes
Araújo, Miguel; Peres, NunoWithin the Hartree Fock RPA analysis, we derive the spin wave spectrum for the weak ferromagnetic phase of the Hubbard model on a honeycomb lattice. Assuming a uniform magnetization, the polar (optical) and acoustic branches of the spin wave excitations are determined. The bipartite lattice geometry produces a q-dependent phase difference between the spin wave amplitudes on the two sub-lattices. We also find an...
Comment on 'Gapless Spin-1 Neutral Collective Mode Branch for Graphite
Peres, Nuno; Araújo, Miguel; Neto, AntónioThe interest in strongly correlated systems in frustrated lattices has been increased recently due to the possible realization of exotic magnetic states, spin, and charge separation in two dimensions, and the discovery of superconductivity in NaxCoO2 yH2O. In a recent Letter, Baskaran and Jafari have proposed the existence of a neutral spin collective mode for a graphene sheet that is modeled as a half-filled H...