Andreev reflection measurements of spin polarization

Abstract

We discuss aspects of Andreev reflection ͑AR͒ measurements in normal metal-superconductor ͑N-S͒ and ferromagnet-superconductor ͑F-S͒ devices. We describe the analytical model used to quantify spin polarization from the conductance measurements and discuss the validity of this simple model using parabolic bands as simple surrogates for real band structures. We present ͑AR͒ measurements of spin polarization in a Cu-Pt-Pb and Co-Pt-Pb lithographically fabricated nanocontact systems where a scattering layer of has been deliberately added to the interface to enable the study of the effect of pair-breaking scattering on AR conductance and spin polarization. We compare these results to the previously published results from clean Cu-Pb and Co-Pb devices and argue that the measurements in devices with the Pt layer can be explained by the presence of inelasticscattering-induced pair-breaking effects. We modify the analytical model to include this effect and show that in some instances, it may be impossible to distinguish between the effects of a finite spin polarization and inelastic scattering. This has implications for AR measurements of spin polarization at disordered or poorly formed F-S interfaces.

Directional point-contact Andreev-reflection spectroscopy of Fe-based superconductors: Fermi surface topology, gap symmetry, and electron–boson interaction

“…In Fe-based superconductors a smaller amplitude of the Andreev signal than in more conventional systems (even multiband, like MgB 2 ) is indeed often (but not always) observed experimentally. However, a similar reduction in the amplitude of the superconducting signal is also expected if the normal bank of the contact is a diffusive metal [37,38], if a large inelastic scattering occurs at the interface [39], if a fraction of the probe current is injected in normal regions (as it can happen if the dopant distribution is inhomogeneous), or even if some Fermi surface sheets are gapless. For the sake of completeness, it must be said that a small Andreev signal is also predicted if the gap is anisotropic (see figure 2).…”

Point-contact Andreev-reflection spectroscopy of doped manganites: Charge carrier spin-polarization and proximity effects (Review Article)

“…(For more details see original reports [14,27,56,57,61,63,64], textbook [12] and recent review [13]. )…”

Continuous control of spin polarization using a magnetic field

“…Experimentally, an interface is often not ideal and a modified Blonder-Tinkham-Klapwijk (BTK) model is often utilized to extract the P value. [24][25][26][27][28] Common superconductors such as Pb and Nb have small critical fields 29 (H C < 1 kOe), which could not be utilized for ARS in this work. Instead, a 0.5-mm NbTi wire was used to fabricate the superconducting tip in these experiments.…”