Efeitos de tamanho em cadeias de Heisenberg-ising com interações antiferromagneticas
AUTOR(ES)
Djalma Medeiros
DATA DE PUBLICAÇÃO
1991
RESUMO
Finite Heisenberg-Ising quantum chains, for spin s = 1/2 and periodic boundary conditions, are exactly solved by numerical methods diagonalizing the Hamiltonian using the Lanczos method up to size N = 28 spins. Interesting physical quantities are computed, including the ground state energy, the mass gap, the spin-wave velocity, and correlation functions. Scaling laws with size are obtained and compared with analytical predictions suggested by Bethe ansatz and conformal invariance. Computational results show that the mass gap closes exponentially with size in the whole anisotropic region. The extrapolated ground state is double degenerate, and displays long-range order with dominant components of the Néel type. Quantum fluctuations are enhanced as the anisotropy is reduced, leading to a singlet ground state without long-range order for the infinite system at the isotropic point. In this regime, size effects have logarithmic corrections. A crossover is predicted in the spin-wave velocity behavior at N ~ 50, well above the available sizes in a typical Lanczos calculation. Tables and plots of the computed quantities are presented along with extrapolated values using standard algorithms
ASSUNTO(S)
principio de incerteza heisenberg antiferromagnetismo
ACESSO AO ARTIGO
http://libdigi.unicamp.br/document/?code=vtls000029218Documentos Relacionados
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