Abstract
The XY model (s = 1/2) on the one-dimensional alternating superlattice
(closed chain) is solved exactly by using a generalized Jordan-Wigner
transformation and the Green function method. Closed expressions are
obtained for the excitation spectrum, the internal energy, the specific
heat, the average magnetization per site, the static susceptibility,
X-zz, and the two-spin correlation function in the field direction at arbitrary temperature. At T = 0, it is shown that the system presents
multiple second-order phase transitions induced by the transverse field,
which are associated to the zero energy mode with wave number equal to 0
or pi. It is also shown that the average magnetization as a function of
the held presents, alternately, regions of plateaux (disordered phases)
and regions of variable magnetization (ordered phases). The static
correlation function presents an oscillating behavior in the ordered
phase and its period goes to infinity at the critical point. (C) 1999 Elsevier Science B.V. All rights reserved.The XY model (s = 1/2) on the
one-dimensional alternating superlattice (closed chain) is solved
exactly by using a generalized Jordan-Wigner transformation and the
Green function method. Closed expressions are obtained for the
excitation spectrum, the internal energy, the specific heat, the average
magnetization per site, the static susceptibility, chi(zz), and the
two-spin correlation function in the field direction at arbitrary temperature. At T = 0, it is shown that the system presents multiple
second-order phase transitions induced by the transverse field, which
are associated to the zero energy mode with wave number equal to 0 or
pi. It is also shown that the average magnetization as a function of the
held presents, alternately, regions of plateaux (disordered phases) and
regions of variable magnetization (ordered phases). The static
correlation function presents an oscillating behavior in the ordered
phase and its period goes to infinity at the critical point. (C) 1999
Elsevier Science B.V. All rights reserved.
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