Journal ArticleDOI
Ising model in a transverse field. I. Basic theory
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TLDR
In this article, a brief review of the spin-iIsing model in a transverse field provides a useful description (insulating magnetic systems, order-disorder ferroelectrics, cooperative Jahn-Teller systems and other systems with 'pseudo-spin'- phonon interactions).Abstract:
A brief review is first made of systems for which the spin-iIsing model in a transverse field provides a useful description (insulating magnetic systems, order-disorder ferroelectrics, cooperative Jahn-Teller systems and other systems with 'pseudo-spin'- phonon interactions). A perturbation expansion is then developed which provides for all temperatures an approximate description of the model. The perturbation series is classified with respect to the small parameter l/z, where z is the number of spins interacting with a given spin; this generates the molecular-field approximation and the random-phase approxi- mation as the lowest-order description of the thermodynamic functions and correlation functions respectively. The leading-order approximations for the correlation functions, susceptibilities and spectral functions are discussed in detail. The formalism, which is the first application of such techniques to systems with varying magnetization direction, provides a basis for subsequent higher-order calculations of the free energy and correlation functions.read more
Citations
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Theory of Ferroelectric Phase Transition in KHzP04 Type Crystals. I
TL;DR: In this article, a theory of the phase transi- tion is developed under the assumption that the ferroelectric behavior of this substance is due to cooperation of the ionic displacements, the interactions between ions and protons and the tunneling motion of protons.
Journal ArticleDOI
Quantum phase transition of a magnet in a spin bath.
Henrik M. Rønnow,Raghuveer Parthasarathy,Jens Jensen,Gabriel Aeppli,Thomas Rosenbaum,Desmond F. McMorrow +5 more
TL;DR: It is found that interactions with the nuclear spin bath controlled the length scale over which the excitations could be entangled, which places a limit on the ability to observe intrinsic electronic quantum criticality.
Journal ArticleDOI
Theory of surface modes in ferroelectrics
TL;DR: In this paper, a theoretical investigation of the possible occurrence of surface modes in semi-infinite ferroelectric materials is made, and three different approaches are used: (1) a microscopic pseudo-spin theory based on the Ising model in a transverse field, (2) a macroscopic Landau theory in which surface effects can be introduced phenomenologically, and (3) a polariton model appropriate to the very long wavelength region.
Journal ArticleDOI
Bayesian approach to cluster expansions
Tim Mueller,Gerbrand Ceder +1 more
TL;DR: A Bayesian framework for developing cluster expansions that explicitly incorporates physical insight into the fitting procedure is presented and methods that significantly improve the predictive power of cluster expansions for a given training set size are developed.
Journal ArticleDOI
The Curie temperature of ultra-thin ferroelectric films
TL;DR: In this paper, the authors studied the Curie temperature of ferroelectric films described by the transverse Ising model under the mean-field theory and obtained the film layer number, the surface interaction and the surface layer number dependence of the curie temperature.
References
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Journal ArticleDOI
The one-dimensional Ising model with a transverse field
TL;DR: In this paper, the one-dimensional Ising model with a transverse field is solved exactly by transforming the set of Pauli operators to a new set of Fermi operators.
Journal ArticleDOI
Collective motions of hydrogen bonds
TL;DR: In this article, the low frequency collective modes of protons are calculated for ferrroelectric crystals of the KH 2 PO 4 type taking into account the tunneling frequency and a simplified interaction between proton sites.
Journal ArticleDOI
Mobility of Edge Dislocations in Silicon‐Iron Crystals
Dale F. Stein,J.R Low +1 more
TL;DR: In this paper, the velocities of unpinned edge dislocations in 3¼% silicon-iron have been measured as a function of stress over a range of five orders of magnitude in velocity from 10−7 cm/sec to 10−2 cm /sec.
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On the isotopic effects in the ferroelectric behaviour of crystals with short hydrogen bonds
TL;DR: In this article, a quantum-mechanical extension of Mason and Devonshire's long-range forces model was proposed to explain the isotopic effects in the ferroelectric properties of hydrogen-bonded crystals.