Fluctuation phenomena in tunnel junctions

ANNALS

OF

PHYSICS

85,

Abstracts

591-592

(1974)

of Papers

to Appear

in Future

Issues

Fluctuation Phenomena in Tunnel Junctions. D. ROGOVIN. Department of Physics and Optical Sciences Center, University of Arizona, Tucson, Arizona, and D. J. SCALAPINO. Department of Physics, University of California, Santa Barbara, California. A general theory of electrodynamic fluctuations in tunnel junctions is developed. Using standard many-body techniques we determine the quasi-particle, pair and quasi-particle-pair current power spectra and show that these current fluctuations are simply related to the associated pieces of the junction l(V) characteristic. In addition a theory of the Josephson radiation linewidth is presented. Critical kattering in A,B Compounds at Structural Transitions. NARINDER K. AILAWADI. Institut fur Theoretische Physik, Freie Universitat Berlin, Berlin, West Germany. A theory of critical scattering in A,B compounds having A 15 structure at structural transitions (martensitic phase transitions) is developed. The theory is based on the assumption that the critical scattering is due to density fluctuations. This primary variable is coupled to current density fluctuations considered as secondary variable. Zwanzig-Mori projection operator technique is used to dIerive equations of motion. The time dependence of the memory function describing the delayed response of the stress tensor due to a change of shear is modelled and is assumed to decay exponentially. This description takes into account elastoviscous effects in solids, and leads, near the transition temperature, to a correct three-pole structure around w = 0 and includes the central peak and the resonances of the conventional soft phonon mode. The central peak is predicted whenever elastoviscous effects are important. Our theory clarifies the phenomenological expressions for the dynamic structure factor proposed by Shirane and Axe. If order-parameter fluctuations were considered to be responsible for the dynamic structure factor, our results would correspond to theories proposed by Schwab1 and Schneider for perovskites. Our paper thus helps clarify and unify the existing theories on critical dynamics at structural transitions in A,B compounds and ABO, perovskites. The Energy Density Formalism and the Shell Structure Ejbcts. M. BEINER AND R. J. LOMBARD. Institut de Physique Nucleaire, Division de Physique Theorique, 91406, Orsay, France. The Brueckner formulation of the energy density formalism has been extended in order to take into account shell structure effects in the description of nuclear bulk properties. The energy density is calculated by using a density dependent effective interaction of the type I’,,, = g(p)6(r, - r2) + p,(r, - Irz). The function g(p) can be determined from nuclear matter calculations. The second term of the interaction is a long range part in the Moszkowski-Scott sense, which is supposed to contribute only in the surface of finite system and for which use is made of the gradient expansion. A phenomenological 1 s term is also included. The nuclear ground states are described by products of neutron and proton BCS wave functions. The pairing matrix elements are derived from a realistic two-body interaction. The ground state properties are obtained by minimizing the total energy with respect to effective single particle orbitals and their corresponding occupation numbers. The variational principle leads to Hartree-Fock-BCS equations which can be solved by iterations. The calculations have been performed for a very large number of nuclei distributed throughout the periodic table. The method is shown to reproduce the bulk nuclear properties

591 Copyright: All rights

0 1974 by Academic Press, Inc. of reproduction in any form reserved.