4,810 research outputs found

### Symmetry of high-piezoelectric Pb-based complex perovskites at the morphotropic phase boundary II. Theoretical treatment

The structural characteristics of the perovskite- based ferroelectric
Pb(Zn1/3Nb2/3)O3-9%PbTiO3 at the morphotropic phase boundary (MPB) region
(x≃0.09) have been analyzed. The analysis is based on the symmetry
adapted free energy functions under the assumption that the total polarization
and the unit cell volume are conserved during the transformations between
various morphotropic phases. Overall features of the relationships between the
observed lattice constants at various conditions have been consistently
explained. The origin of the anomalous physical properties at MPB is discussed

### Sum Rule of the Hall Conductance in Random Quantum Phase Transition

The Hall conductance $\sigma_{xy}$ of two-dimensional {\it lattice} electrons
with random potential is investigated. The change of $\sigma_{xy}$ due to
randomness is focused on. It is a quantum phase transition where the {\it sum
rule} of $\sigma_{xy}$ plays an important role. By the {\it string} (anyon)
gauge, numerical study becomes possible in sufficiently weak magnetic field
regime which is essential to discuss the floating scenario in the continuum
model. Topological objects in the Bloch wavefunctions, charged vortices, are
obtained explicitly. The anomalous plateau transitions ($\Delta \sigma_{xy}=
2,3,... >1$) and the trajectory of delocalized states are discussed.Comment: 7 pages RevTeX, 4 postscript figures, to appear in Physical Review
Letter

### Lattice chiral symmetry, Yukawa couplings and the Majorana condition

It is shown that the conflict between lattice chiral symmetry and the Majorana condition in the presence of Yukawa couplings, which was noted in our previous paper, is related in an essential way to the basic properties of Ginsparg-Wilson operators, namely, locality and species doubling

### On Phase Transition of $NH_{4}H_{2}PO_{4}$-Type Crystals by Cluster Variation Method

The Cluster Variation Method (CVM) is applied to the Ishibashi model for
ammonium dihydrogen phosphate ($\rm NH_{4}H_{2}PO_{4}$) of a typical hydrogen
bonded anti-ferroelectric crystal. The staggered and the uniform susceptibility
without hysteresis are calculated at equilibrium. On the other hand, by making
use of the natural iteration method (NIM) for the CVM, hysteresis phenomena of
uniform susceptibility versus temperature observed in experiments is well
explained on the basis of local minimum in Landau type variational free energy.
The polarization $P$ curves against the uniform field is also calculated.Comment: 14 pages, 10 figure

### Static dielectric response and Born effective charge of BN nanotubes from {\it ab initio} finite electric field calculations

{\it Ab initio} investigations of the full static dielectric response and
Born effective charge of BN nanotubes (BN-NTs) have been performed for the
first time using finite electric field method. It is found that the ionic
contribution to the static dielectric response of BN-NTs is substantial and
also that a pronounced chirality-dependent oscillation is superimposed on the
otherwise linear relation between the longitudinal electric polarizability and
the tube diameter ($D$), as for a thin dielectric cylinderical shell. In
contrast, the transverse dielectric response of the BN-NTs resemble the
behavior of a thin (non-ideal) conducting cylindrical shell of a diameter of
$D+4$\AA, with a screening factor of 2 for the inner electric field. The
medium principal component $Z_y^*$ of the Born effective charge corresponding
to the transverse atomic displacement tangential to the BN-NT surface, has a
pronounced $D$-dependence (but independent of chirality), while the large
longitudinal component $Z_z^*$ exhibits a clear chirality dependence (but
nearly $D$-independent), suggesting a powerful way to characterize the diameter
and chirality of a BN-NT.Comment: submitted to PR

### The quantum space-time of c=-2 gravity

We study the fractal structure of space-time of two-dimensional quantum
gravity coupled to c=-2 conformal matter by means of computer simulations. We
find that the intrinsic Hausdorff dimension d_H = 3.58 +/- 0.04. This result
supports the conjecture d_H = -2 \alpha_1/\alpha_{-1}, where \alpha_n is the
gravitational dressing exponent of a spinless primary field of conformal weight
(n+1,n+1), and it disfavours the alternative prediction d_H = 2/|\gamma|. On
the other hand ~ r^{2n} for n>1 with good accuracy, i.e. the boundary
length l has an anomalous dimension relative to the area of the surface.Comment: 46 pages, 16 figures, 32 eps files, using psfig.sty and epsf.st

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