Regensburg 2022 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 26: Superconductivity: Tunnelling and Josephson Junctions

TT 26.6: Vortrag

Donnerstag, 8. September 2022, 10:45–11:00, H10

The DC Josephson effect for a single level weak link: a Green’s function formulation within a particle conserving theory of superconductivity — •Anton Bleibaum and Milena Grifoni — Institute for Theoretical Physics, University of Regensburg, 93053 Regensburg, Germany

In traditional transport set-ups a current only flows when a bias voltage is applied. In the presence of superconducting electrodes a super-current can flow through a tunneling barrier even in thermodynamic equilibrium. This phenomenon is called DC-Josephson effect. Most of its features can be captured within mean field BCS-theory, according to which the supercurrent is a function of the phase difference between the two superconductors.

How can this result be reconciled with charge conservation in a physical system? In this work we compute the DC Josephson current in transport set-ups consisting of two superconducting electrodes coupled to a single level non-interacting quantum dot. The computation is based on a particle conserving theory of superconductivity. We first provide a current formula in terms of particle conserving Green’s functions. In a second step the infinite hierarchy of equations for the relevant Green’s function is solved. The Andreev bound states spectrum naturally follows from the poles of the retarded Green’s function, and the DC-current has the form known from BCS theory.