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GREEN'S QUANTUM TEMPERATURE FUNCTIONS

Sh. M. Kogan

Published May 21, 1959• 0 citations
OpenAlex

Abstract

The thermodynamic properties of quantum systems are studied by the method of Green's function generalization for systems with arbitrary temperatures T > O. The quasi-closed system of Fermi particles with electromagnetic interaction is analyzed. (R.V.J.)

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The individual particle theory of many body systems was studied starting from a microscopic point of view. A technique which is equivalent to a generalized thermodynamics was used to show that, under the appropriate conditions of temperature and external field, the quasi-particle approach is correct for three very dissimilar systemsi the normal degenerate Fermi system, the metallic electron-phonon system, and the polaron. The fact that an approach like this works for such dissimilar systems emphasizes the underlying unity of the quasi-particle models. The concept that the real t~me non-equilibrium self-energy and the incoherent part of the density-density correlation function may be generated as functional derivatives of a generalized thermodynamic potential (~), together with local translational and rotational invariance and Galilean relativity, leads to a transformation from the microscopic particle density variables g«p,m,R,T) to those of the quasi-particle theory n (R,T). ~ - p- It was shown that, for zero temperature, such a ~ derivability is exact; at low temperature and for slowly varying fields, this ~ derivability is approximately true. This was shown by a procedure which is eqUivalent to an expansion in terms of the real scattering probability for quasiparticles. At low temperature and for slowly varying fields, such real scattering is very improbable and the expansion parameter is small. Perturbation theory was used only to determine the actual size of terms which, on physical grounds are necessarily small. As such, this approach is non-perturbative, depending only on properties of the exact selfenergies and correlation functions. In addition to demonstrating that the quasi-particle models are correct, information on the regions of validity for ~hese models is obtained. .As by-products of these derivations, microscopic expressions for the parameters of the quasi-particle theory and simple microscopic expressions for the currents in degenerate Fermi systems and the electron-phonon system are obtained.
This article is devoted to the theoretical investigation of processes in macroscopic systems based on wave particle duality and quantum statistical distributions using the Green’s function method. In particular, it pro vides a detailed description of the properties and characteristics of the Green’s function for an ideal Fermi liquid, single- and two-particle Green’s functions, as well as Green’s functions at limiting temperatures and for the Dirac and Schrödinger equations. The study analyzes the application of the Green’s function method to processes in many-particle quantum systems and to solving equations that describe the constituent particles of such systems. For a given operator and set of boundary conditions, a Green’s function can be defined, al lowing the solution of the corresponding equation to be expressed in integral form. A distinctive feature of this method is the application of mathematical-physics tools, such as Fourier methods, integral transforms, special functions, and mathematical analysis, to problems in quantum physics governed by the principles of quantum and statistical mechanics. The relevance of this study stems from the application of the Green’s function method to the analysis of quantum phenomena. This approach is considered one of the effective methods for solving partial differential equations describing various physical processes. It involves transform ing the original differential equation into an equivalent integral equation involving Green’s functions, which can then be solved. The transformation involves passing to the momentum representation and applying Fouri er transforms using methods of complex analysis.