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Journal of the Physical Society of Japan

Dynamics and Statistical Mechanics of the Classical Ising Model in a Transverse Field II

Shigeo Homma, Shôzô Takeno

Published Sep 15, 1981• 3 citations
Publisher

Abstract

Dynamics and statistical mechanics of kinks in one-dimensional classical Ising model in a transverse field is studied in a dilute kink-gas approximation along the line with the theory of Krumhansl and Schrieffer. The energy of a single kink is written in a simple analytic form by approximating an exact one-kink solution. Kinks in the system are then treated as gas of quasi-particles. It is shown that the partition function so obtained is coincident with that of the result obtained previously by using the transfermatrix method. The dynamical structure of the system is also calculated to show the existence of central peak due to kink excitations.

DOI
10.1143/jpsj.50.2818

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Dynamics and statistical mechanics of kinks in one-dimensional classical Ising model in a transverse field is studied in a dilute kink-gas approximation along the line with the theory of Krumhansl and Schrieffer. The energy of a single kink is written in a simple analytic form by approximating an exact one-kink solution. Kinks in the system are then treated as gas of quasi-particles. It is shown that the partition function so obtained is coincident with that of the result obtained previously by using the transfermatrix method. The dynamical structure of the system is also calculated to show the existence of central peak due to kink excitations.
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On the basis of the effective Hamiltonian method the static properties of the transverse Ising model with substitutional disorder have been investigated. By a perturbation expansion of the density matrix the self-consistent equation for the effective field is obtained in an analytical form. The transition temperature and the susceptibility etc. are derived from the partition function and numerically calculated. It is shown that for the diluted systems this approximation gives much lower transition temperatures and higher critical concentrations than the simple ones previously derived. In the two-component system with a strong transverse field a finite critical concentration is predicted in contrast to the previous studies. The application of this approximation to the “pseudo” one-dimensional systems having weak interchain correlations is also discussed.
The dynamics of the three-dimensional anisotropic spin-\textonehalf{} Ising model in a transverse field is studied above Tc{T}_{c}Tc​ by a method in which the coupled-chain problem is reduced to that of a single chain in an effective field. The problem of a single chain is studied by means of Mori's continued-fraction expansion in a four-pole approximation. The moments are obtained by using the time-dependent correlation function calculated in the ccc-cyclic and in the improved ccc-cyclic approximations [J. Phys. A 13, 223 (1980)]. A comparison between these two approximations is done by calculating the critical temperature as function of the tunneling field. The one-dimensional correlation length is obtained, and it agrees well with the experimental results for the quasi-one-dimensional ferroelectric CsD2{\mathrm{D}}_{2}D2​PO4{\mathrm{O}}_{4}O4​.
An exact description of integrable spin chains at finite temperature is provided using an elementary algebraic approach in the complete Hilbert space of the system. We focus on spin chain models that admit a description in terms of free fermions, including paradigmatic examples such as the one-dimensional transverse-field quantum Ising and XY models. The exact partition function is derived and compared with the ubiquitous approximation in which only the positive parity sector of the energy spectrum is considered. Errors stemming from this approximation are identified in the neighborhood of the critical point at low temperatures. We further provide the full counting statistics of an arbitrary observable at thermal equilibrium and characterize in detail the thermal distribution of the kink number and transverse magnetization in the transverse-field quantum Ising chain.
An exact description of integrable spin chains at finite temperature is provided using an elementary algebraic approach in the complete Hilbert space of the system.We focus on spin chain models that admit a description in terms of free fermions, including paradigmatic examples such as the one-dimensional transverse-field quantum Ising and XY models.The exact partition function is derived and compared with the ubiquitous approximation in which only the positive parity sector of the energy spectrum is considered.Errors stemming from this approximation are identified in the neighborhood of the critical point at low temperatures.We further provide the full counting statistics of a wide class of observables at thermal equilibrium and characterize in detail the thermal distribution of the kink number and transverse magnetization in the transverse-field quantum Ising chain.
An exact description of integrable spin chains at finite temperature is provided using an elementary algebraic approach in the complete Hilbert space of the system. We focus on spin chain models that admit a description in terms of free fermions, including paradigmatic examples such as the one-dimensional transverse-field quantum Ising and XY models. The exact partition function is derived and compared with the ubiquitous approximation in which only the positive parity sector of the energy spectrum is considered. Errors stemming from this approximation are identified in the neighborhood of the critical point at low temperatures. We further provide the full counting statistics of a wide class of observables at thermal equilibrium and characterize in detail the thermal distribution of the kink number and transverse magnetization in the transverse-field quantum Ising chain.