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 NH4H2PO4NH_{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