The phase transition properties of a ferroelectric superlattice
described by the Ising model in a transverse field have been
investigated using the effective-field theory with a probability
distribution technique that accounts for the self-spin correlation
functions. An independent interface plane has been assumed and the
parameters that imitate BaTiO3/SrTiO3 structure have been used
in our calculation. The Curie temperature, polarization, and
dielectric constant have been obtained. The most striking feature
is that the dielectric constant presents a maximum at room
temperature. This kind of feature has been observed in a recent
experimental measurement.
Within the framework of the effective-field theory, we examine the phase transitions of a transverse spin-1 Ising film. We discuss an L
-layer film of simple cubic symmetry with nearest-neighbour exchange interactions in which the exchange interaction strengths in surface layers are assumed to be different from the bulk values, and we derive and illustrate expressions for the phase diagrams and order parameter profiles. It is found that for a ratio of the surface exchange interactions to the bulk ones R
= Js
/J
less than a critical value Rc
, the critical temperature Tc
/J
of the film is smaller than the bulk critical temperature Tc
B
/J
and, as L
is increased further, Tc
/J
increases. However, for R
>Rc
, Tc
/J
is greater than the bulk critical temperature Tc
B
/J
and, as L
is increased further, Tc
/J
decreases.
Structure of eight superdeformed bands in the nucleus 151 Tb is analyzed using the results of the Hartree-Fock and Woods-Saxon cranking approaches. It is demonstrated that far going similarities between the two approaches exist and predictions related to the structure of rotational bands calculated within the two models are nearly parallel. An interpretation scenario for the structure of the superdeformed bands is presented and predictions related to the exit spins are made. Small but systematic discrepancies between experiment and theory, analyzed in terms of the dynamical moments, J (2) , are shown to exist. The pairing correlations taken into account by using the particle-numberprojection technique are shown to increase the disagreement. Sources of these systematic discrepancies are discussed -they are most likely related to the yet not optimal parametrization of the nuclear interactions used. This is so, because the abrupt band crossings (relatively abundant in other nuclei) may otherwise cause strong variations of J (2) -moments as a function of ω, thus rendering the
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