Flow equations for electron-phonon interactions

Mario Ragwitz, Franz Wegner

A. Hübsch, K. W. Becker

Peter Lenz, Franz Wegner

A recently [9] proposed method of continuous unitary transformations is used to eliminate the interaction between electrons and phonons. The differential equations for the couplings represent an infinitesimal formulation of a sequence of Fröhlichtransformations [5]. The two approaches are compared. Our result will turn out to be less singular than Fröhlich’s. Furthermore the interaction between electrons belonging to a Cooper-pair will always be attractive in our approach. Even in the case where Fröhlich’s transformation is not defined (Fröhlich actually excluded these regions from the transformation), we obtain an elimination of the electron-phonon interaction. This is due to a sufficiently slow change of the phonon energies as a function of the flow parameter. 1 New address: Max-Planck-Institut für Kolloid- und Grenzflächenforschung, Kantstraße 55,

Wilfried Schäfer, Martin Wegener

Boon-Kok Tan, G. Yassin, Phichet Kittara +1 more

The heating of SIS tunnel junctions by local oscil- lator (LO) power and bias voltage is well known and has been reported previously. In this paper, we present a novel method for recovering the heating parameters from the experimental pumped I-V curves of an SIS device at 700 GHz, together with the coupled LO power and the embedding impedance. Since this is obtained without assuming a particular power law between LO power and junction temperature, we will be able to find ?eph, the electron-phonon interaction time of the superconducting material at various bath temperatures. We would deduce a power law that describes the dependence of the heat flow equation on temperature. Index Terms—Superconductor-insulator-superconductor de- vices, electron-phonon interaction time, heat flow, power law.