Based on the analysis of 13 million price records underlying the computation of the French consumer price index, we provide a detailed assessment of consumer price rigidity. Our main results are as follows. The average duration of prices is around 8 months. Price durations and the patterns of price-setting strongly differ across sectors. Price cuts are almost as frequent as increases, suggesting no specific downward nominal rigidity. Price changes typically have large absolute sizes. Time variation in the frequency of price changes and in their size both contribute to inflation fluctuations. Overall there is evidence of both time- and state-dependent price-setting. Copyright Blackwell Publishing Ltd and the Department of Economics, University of Oxford 2007.

No abstract

The tunability of electrical polarization in ferroelectrics is instrumental to their applications in information-storage devices. The existing ferroelectric memory cells are based on the two-level storage capacity with the standard binary logics. However, the latter have reached its fundamental limitations. Here we propose ferroelectric multibit cells (FMBC) utilizing the ability of multiaxial ferroelectric materials to pin the polarization at a sequence of the multistable states. Employing the catastrophe theory principles we show that these states are symmetry-protected against the information loss and thus realize novel topologically-controlled access memory (TAM). Our findings enable developing a platform for the emergent many-valued non-Boolean information technology and target challenges posed by needs of quantum and neuromorphic computing.

Ferroelectric properties of thin film materials like lead zirconate titanate differ from those observed for bulk material. It is well known that the surface can strongly influence phase transition phenomena. By the use of a thermodynamical approach, very similar to those generally used to describe phase transitions, we have proposed for studying ferroelectric states a two dimensional lattice model which allowed us to account for surface effects. These surface effects described by an inhomogeneous Landau–Devonshire theory were suggested to produce a finite size effect even if the surface charge is compensated at the metallic electrodes. The manifestations of the field induced by the bound charges in the polarization switching is discussed and is shown to depend strongly on the bulk correlation length and on the extrapolation length. Finally we have applied our model to investigate the influence of the surface effect and of the related bound charges on the thickness dependence of ferroelectric properties.

During ion etching (IE) processes used for making a Pt electrode in the fabrication of ferroelectric capacitors, the film is exposed to radiation and energetic ion bombardment. The influence of such processes on polarization-electric field characteristics of lead zirconate titanate thin film capacitor has been reported by E. G. Lee [Appl. Phys. Lett. 69, 1223 (1996)]. A large field shift and a constriction in the hysteresis loop are experimentally observed. For these authors, this behavior is probably due to the existence of space charges trapped near electrodes. For a better understanding of these phenomena, we have developed a model of ferroelectric capacitor based on the phenomenological Landau–Devonshire theory. A two-dimensional lattice of dipoles is assumed to describe the film. By solving Poisson’s equation, the electric-field distribution inside the film is calculated, which allows us to locally determine the evolution of the polarization by minimizing free energy. IE effects and probably the existence of space charges in the film are introduced by means of a doping layer in the film near the electrode. The influence of important parameters such as doping level, and thickness of the doped layer on the hysteresis loop are investigated. Main experimental thin film electric behaviors are well reproduced and explained considering dipoles switched inside the lattice. Results are interpreted by splitting the hysteresis loop deformation into two effects with different origins: a constriction effect related to the number of impurities inside the film and a shift effect related to the asymmetrical impurities distribution.

Reducing thickness of ferroelectric films typically comes with an apparent degradation of their ferroelectric and dielectric properties. The existence of low-dielectric interfacial layers is often invoked to explain such behaviors. Much work has been done on modeling ferroelectric thin films by considering a ferroelectric layer between two layers with low dielectric constant. In these models it is necessary to introduce extrinsic parameters; the dielectric constant and the polarization are step functions of the depth inside the film. We have developed a model for ferroelectric semiconductors based on the inhomogeneous Landau-Devonshire theory, including surface effects. The local electric field is determined by solving Poisson's equation in which a differential permittivity replaces the dielectric constant. We have found that the hysteresis loops were strongly influenced by the correlation length. That point is discussed by examining the electric field, polarization, and differential permittivity profile inside the film. It is shown that the differential permittivity strongly decreases with the correlation length increases. That phenomena leads to high electric fields inside the film and especially close to the surface. As a consequence, an explanation for thin film ferroelectric properties can be given by invoking space charge density many orders of magnitude lower than those usually considered.

As a first approach to the study of strained pseudomorphic materials, we have used a Monte Carlo method to calculate the effect of strain on electron transport properties of bulk InGaAs. Strain-induced velocity reduction is found to be much more pronounced for InGaAs grown on GaAs substrate than for InGaAs grown on InP substrate.

No abstract