0000000001044735
AUTHOR
Elia Strambini
Superconductor-ferromagnet hybrids for non-reciprocal electronics and detectors
We review the use of hybrid thin films of superconductors and ferromagnets for creating non-reciprocal electronic components and self-biased detectors of electromagnetic radiation. We start by introducing the theory behind these effects, as well as different possible materials that can be used in the fabrication of these components. We proceed by discussing in detail the fabrication and characterization of Al/EuS/Cu and EuS/Al/Co based detectors, along with their noise analysis. We also indicate some routes for multiplexing such self-biased detectors.
Coexistence of superconductivity and spin-splitting fields in superconductor/ferromagnetic insulator bilayers of arbitrary thickness
Ferromagnetic insulators (FI) can induce a strong exchange field in an adjacent superconductor (S) via the magnetic proximity effect. This manifests as spin splitting of the BCS density of states of the superconductor, an important ingredient for numerous superconducting spintronics applications and the realization of Majorana fermions. A crucial parameter that determines the magnitude of the induced spin splitting in FI/S bilayers is the thickness of the S layer d: In very thin samples, the superconductivity is suppressed by the strong magnetism. By contrast, in very thick samples, the spin splitting is absent at distances away from the interface. In this work, we calculate the density of …
InAs nanowire superconducting tunnel junctions: spectroscopy, thermometry and nanorefrigeration
We demonstrate an original method -- based on controlled oxidation -- to create high-quality tunnel junctions between superconducting Al reservoirs and InAs semiconductor nanowires. We show clean tunnel characteristics with a current suppression by over $4$ orders of magnitude for a junction bias well below the Al gap $\Delta_0 \approx 200\,\mu {\rm eV}$. The experimental data are in close agreement with the BCS theoretical expectations of a superconducting tunnel junction. The studied devices combine small-scale tunnel contacts working as thermometers as well as larger electrodes that provide a proof-of-principle active {\em cooling} of the electron distribution in the nanowire. A peak ref…
Charge transport through spin-polarized tunnel junction between two spin-split superconductors
We investigate transport properties of junctions between two spin-split superconductors linked by a spin-polarized tunneling barrier. The spin-splitting fields in the superconductors (S) are induced by adjacent ferromagnetic insulating (FI) layers with arbitrary magnetization. The aim of this study is twofold: On the one hand, we present a theoretical framework based on the quasiclassical Green's functions to calculate the Josephson and quasiparticle current through the junctions in terms of the different parameters characterizing it. Our theory predicts qualitative new results for the tunneling differential conductance, $dI/dV$, when the spin-splitting fields of the two superconductors are…
Thermoelectric Radiation Detector Based on Superconductor-Ferromagnet Systems
We suggest an ultrasensitive detector of electromagnetic fields exploiting the giant thermoelectric effect recently found in superconductor-ferromagnet hybrid structures. Compared with other types of superconducting detectors where the detected signal is based on variations of the detector impedance, the thermoelectric detector has the advantage of requiring no external driving fields. This is especially relevant in multipixel detectors, where the number of bias lines and the heating induced by them are an issue. We propose different material combinations to implement the detector and provide a detailed analysis of its sensitivity and speed. In particular, we perform a proper noise analysis…