Peculiarity of non-equilibrium superconductivity in half-metallic ferromagnet/insulator/superconductor Co2CrAl/I/Pb heterostructures

Shlapak

et al. 2011

The giant spin blocking of tunnel currents discovered by us (Low. Temp. Phys. 36, 186 (2010)) is investigated theoretically and experimentally in ferromagnet F (Co2CrAl)- insulator I- superconductor S (Pb) heterostructures with a wide range of specific resistances (10−7–10−4 Ω · cm2). The magnitude of this effect is found to depend on the specific resistance of the junction in the normal state and on recombination spin depolarization. A theoretical model which provides an adequate description of the tunnelling of spin-polarized electrons in F-I-S junctions is proposed. It is found that the normalized conductivity σFS of an F-I-S tunnel junction can be considerably lower than the fundamental normalized conductivity σNS of an N-I-S junction (where N is a normal metal). The proposed model is used to estimate the degree of spin polarization p of films of the ferromagnetic semimetal Co2CrAl (Heusler alloy) with B2- and L21-type crystal structures, which is close to 1 (p ≈ 0.97). The temperature dependence σFS(T) of a Co2CrAl-I-Pb F-I-S tunnel junction is studied experimentally. A theoretical model is proposed which provides an adequate description of the temperature behavior of the normalized conductivity σFS(T) with features of spin-polarized tunnelling taken into account.

Section: A Normalized Conductivity R Fs Of F-i-s Junctionsmentioning

confidence: 96%

Tunnel spin injection and the conductivity of ferromagnet-superconductor heterostructures with zero bias

Shlapak

et al. 2011

Current-voltage characteristics of the double tunnel junctions Co2CrAl–I–Pb/Sn–I–Pb under spin-polarized tunnel injection

Krakovnyi

et al. 2012

Current-voltage characteristics and existence features of a superconducting state under the action of tunneling injection of the spin-polarized current Iinj with a high spin polarization degree (p ≈ 0.97) were studied in double tunneling junctions ferromagnet-insulator-superconductor-insulator-superconductor Co2CrAl–I–Pb/Sn–I–Pb. An empirical formula was proposed for describing a dependence of the energy gap Δ on Iinj. A new spin-polarized inhomogeneous superconducting state consisting of superconducting and resistive regions was found. An existence of the proximity effect through a tunnel barrier between ferromagnetic and superconducting films was established. An effective recombination time of spin-polarized quasiparticles in the nonequilibrium superconductor Pb was estimated.

Current-voltage characteristics of low-resistance tunnel structures ferromagnet-insulator-superconductor Co2CrAl–I–Pb

Shlapak

et al. 2013

A physical model of tunneling processes leading to a nonequilibrium superconducting state in ferromagnet-superconductor junctions is proposed and confirmed experimentally. The model is based on the analysis of experimental current-voltage characteristics and the determination of junction voltage dependences of the energy gap, the effective chemical potential and the effective temperature of quasiparticles in the modified energy distribution of quasiparticles as well as on taking into account the change in the density of electron states due to destruction of the Cooper pairs, caused by the proximity effect.