Feynman, R. P. and Hellwarth, R. W. and Iddings, C. K. and Platzman, P. M. (1962) Mobility of slow electrons in a polar crystal. Physical Review, 127 (4). pp. 10041017. ISSN 0031899X. http://resolver.caltech.edu/CaltechAUTHORS:FEYpr62

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Abstract
We have obtained an approximate expression for the impedance function at all frequencies, temperatures, and coupling strengths of an electron coupled to a polar lattice (a system commonly called a polaron). The starting point for the calculation is the quantum mechanical expression for the expected current. The phonon coordinates are eliminated from this expression by wellknown fieldtheory techniques. The resulting exact "influence functional" is then approximated by a corresponding quadratic "influence functional" which, it is hoped, imitates the real polaron. Correction terms are computed to account for the difference between the approximate impedance and the exact polaron impedance in a manner closely analogous to Feynman's treatment of the polaron selfenergy. In fact, the analytic evaluation of the expression for the impedance obtained here is carried out using the approximate "influence functional" that was successfully employed in minimizing the binding (and free) energy of the polaron in earlier calculations. However, the accuracy obtained using this approximation, for the impedance calculation, is less satisfactory and its limitations are discussed. Nevertheless, beginning at intermediate coupling strengths, the approximate impedance produces a level structure of increasing complexity and narrowing resonances as the coupling strengthens. This suggests that further refinements may be fruitful. Methods for finding a better quadratic influence functional for use in our impedance expression as well as ways of improving the expression further are suggested. A comparison of our results with those of the Boltzmann equation points up interesting differences which arise from reversing the order of taking limits of zero frequency and coupling.
Item Type:  Article 

Additional Information:  ©1962 The American Physical Society. Received 26 March 1962. The authors would like to thank W. G. Wagner, Morrel Cohen, J. McKenna, and M. Lax for many helpful and stimulating discussions. 
Issue or Number:  4 
Record Number:  CaltechAUTHORS:FEYpr62 
Persistent URL:  http://resolver.caltech.edu/CaltechAUTHORS:FEYpr62 
Alternative URL:  http://dx.doi.org/10.1103/PhysRev.127.1004 
Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  3552 
Collection:  CaltechAUTHORS 
Deposited By:  Tony Diaz 
Deposited On:  14 Jun 2006 
Last Modified:  26 Dec 2012 08:55 
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