Origin of spin incommensurability in hole-doped S=1 Y2-xCaxBaNiO5 chains

Spin incommensurability (IC) has been recently experimentally discovered in the hole-doped Ni-oxide chain compound Y2-xCaxBaNiO5 [G. Xu et al., Science 289, 419 (2000)]. Here a two orbital model for this material is studied using computational techniques. Spin IC is observed in a wide range of densities and couplings. The phenomenon originates in antiferromagnetic correlations across holes dynamically generated to improve hole movement, as it occurs in the one-dimensional Hubbard model and in recent studies of the two-dimensional extended t-J model. The close proximity of ferromagnetic and phase-separated states in parameter space is also discussed.

Conservation laws for Z(N) symmetric quantum spin models and their exact ground state energies

We derive an infinite set of conserved charges for some Z(N) symmetric quantum spin models by constructing their Lax pairs. These models correspond to the Potts model, Ashkin-Teller model and the particular set of self-dual Z(N) models solved by Fateev and Zamolodchikov [6]. The exact ground state energy for this last family of hamiltonians is also presented. © 1986.

Nuclear magnetic relaxation for the spin-degenerate Anderson model

A renormalization-group calculation of the temperature-dependent nuclear spin relaxation rate for a magnetic impurity in a metallic host is reported. The calculation follows a simplified procedure, which produces accurate rates in the low-temperature Fermi-liquid regime, although yielding only qualitatively reliable results at higher temperatures. In all cases considered, as the temperature T diminishes, the rates peak before decaying linearly to zero in the Fermi-liquid range. For T → 0, the results agree very well with Shiba's expression relating the low-temperature coefficient of the relaxation rate to the squared zero-temperature susceptibility. In the Kondo limit, the enhanced susceptibility associated with the Kondo resonance produces a very sharp peak in the relaxation rate near the Kondo temperature. © 1991.

Espalhamento coulombiano relativístico próximo das condições de simetria de spin e pseudospin

Pós-graduação em Física - FEG

Estudos de acoplamento spin-órbita em dinâmica do sistema solar

Pós-graduação em Física - FEG

On the question of neutrino spin precession in a magnetic field

Using the Feynman procedure of ordered exponential operators we solve the evolution equations for a two-neutrino system considering arbitrarily varying matter density and magnetic field along the neutrino trajectory. We show that a large geometrical phase velocity suppresses νL→νR transitions unless some stationary trajectory is found along the neutrino path. Concerning the solar neutrino case, if we admit the standard solar model matter distribution, no such trajectory can be found.

Quantização de partículas com spin

Pós-graduação em Física - IFT

Simulação de Monte Carlo: de modelos de spin à teoria de campos na rede

Pós-graduação em Física - IFT

Uma abordagem de potencial e massa efetiva e a descrição de espaço de fase quântico para tratar sistemas de spins: Caracterizando o tunelamento de spin e propriedades da molécula de Fe8

Pós-graduação em Física - IFT

Ressonâncias planetárias spin-órbita com perturbação de terceiro corpo

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)