Giant josephson current through a single bound state in a superconducting tunnel junction

Abstract

We study the microscopic structure of the Josephson current in a single-mode tunnel junction with a wide quasiclassical tunnel barrier. In such a junction each Andreev bound state carries a current of magnitude proportional to the amplitude of the normal electron transmission through the junction. Tremendous enhancement of the bound state current is caused by the resonance coupling of superconducting bound states at both superconductor-insulator interfaces of the junction. The possibility of experimental observation of the single bound state current is discussed.Typeset using REVT E X 1

Controlling Josephson transport by manipulation of Andreev levels in ballistic mesoscopic junctions

“…(4), originating from two Andreev bands with anomalously large dispersion, E(φ) ∼ √ D, will dominate the current [6,9]. Because of this large dispersion, the currents of the individual Andreev bound states will exceed the Ambegaokar-Baratoff critical current [23], the sum current in Eq.…”

“…As long as the top of the low-transparency barrier does not pass above the Fermi level µ, the junction will essentially behave as a short SNS junction, with a symmetric pair of dispersing Andreev levels around the Fermi level. Not until the barrier becomes significantly higher than the Fermi level does the junction approach SIS behaviour [9,10].…”

“…Because of this large dispersion, the currents of the individual Andreev bound states will exceed the Ambegaokar-Baratoff critical current [23], the sum current in Eq. [9]. The dephasing parameter β can then be directly related to the electronhole wave vector difference δκ = κ + − κ − , where κ ± = 2m * (V g − µ ± E).…”

“…To illustrate a typical situation, let us assume that the tunnel barrier is about twice as high as the Fermi energy, V g ≈ 2µ. The dephasing parameter β is then given by [9] …”

“…If this barrier is pushed above the Fermi level the transparency will vanish, D → 0, and the junction will essentially become divided into two isolated SI systems, each having a localized Andreev surface/interface state sitting in the gap close to each gap edge [9]. If we now decrease the length of the barrier to allow tunneling, D ≪ 1 but finite, the degenerate SI interface states begin to interact through the tunnel barrier, and we get an SIS junction.…”