Theory of superconductor-ferromagnet point-contact spectra: The case of strong spin polarization

Abstract

We study the impact of spin-active scattering on Andreev spectra of point contacts between superconductors(SCs) and strongly spin-polarized ferromagnets(FMs) using recently derived boundary conditions for the Quasiclassical Theory of Superconductivity. We describe the interface region by a microscopic model for the interface scattering matrix. Our model includes both spin-filtering and spin-mixing and is non-perturbative in both transmission and spin polarization. We emphasize the importance of spin-mixing caused by interface scattering, which has been shown to be crucial for the creation of exotic pairing correlations in such structures. We provide estimates for the possible magnitude of this effect in different scenarios and discuss its dependence on various physical parameters. Our main finding is that the shape of the interface potential has a tremendous impact on the magnitude of the spin-mixing effect. Thus, all previous calculations, being based on delta-function or box-shaped interface potentials, underestimate this effect gravely. As a consequence, we find that with realistic interface potentials the spin-mixing effect can easily be large enough to cause spin-polarized sub-gap Andreev bound states in SC/sFM point contacts. In addition, we show that our theory generalizes earlier models based on the Blonder-Tinkham-Klapwijk approach.

The critical current reaction on hydrostatic pressure of a superconductor–semimetal composite

“…[1][2][3][4][5][6][7][8][9][10][11][12] However, despite a vast number of works on the proximity effect in superconductor-ferromagnet junctions, the critical current has been determined only in a few cases. [13][14][15][16][17] The studies have been mostly limited to the measurements of the temperature dependences in heterostructures, which is largely due to the difficulty of measuring the current-voltage characteristics (CVC) in a direction normal to the thin layers.…”

Comment on “Unified Formalism of Andreev Reflection at a Ferromagnet/Superconductor Interface”

“…Here, we show that while there are numerous works [2][3][4][5][6][7] correctly solving the problem formulated in Ref.…”

“…Regarding (a) and (b), the derivation in Ref. [3] and in other works [4][5][6][7] is rigorous for any P. Regarding (c), one cannot define a single channel BTK model with an arbitrary P [11]: any given electron in a metal Andreev reflects into either a propagating or evanescent wave. Finite P means that while some current-carrying electrons propagate, others evanesce; one can only define spin polarization in a multielectron system, where the numbers of states at the Fermi surface (FS) (conductivity channels) for the two spin directions differ.…”

P-wave Cooper pair splitting

“…Therefore, in a second step we show how p-wave splitting can be realized without using a p-wave superconductor. Indeed, the previous works on the charge transfer statistics of superconductor ferromagnet beamsplitters [10,27–28] neglected the recently predicted [29–31] and observed [32–33] effects of the interface on charge transfer. By including a better description of the interface one can describe the shared triplet pairs formation between the ferromagnets.…”