Fabrication of YBa2Cu3O7−δ/SrTiO3/La0.7Sr0.3MnO3−δ junctions for the control of supercurrent by spin-polarized quasiparticle current injection

Abstract

Supercurrent suppression by the injection of spin-polarized quasiparticle current from a ferromagnet into a superconductor is demonstrated in YBa2Cu3O7−δ/SrTiO3/La0.7Sr0.3MnO3−δ junctions at 77 K. Negative current gains as large as 35 have been observed. The magnitude of the effect depends on the net polarization of the injection current, film resistivities, barrier microstructure, and injection geometry. Fabrication of the junctions is discussed in terms of optimizing these parameters for maximum supercurrent suppression.

Spin relaxation in mesoscopic superconducting Al wires

“…Measurements of spin accumulation effect in F/S/F-type bipolar spin transistors 19 showed an increase of the spin-diffusion length in superconducting Nb films as λ sp (T ) = λ sp (0)/(1 − T /T c ) n with 1/4 < n < 1/2, with increasing temperature below the superconducting transition temperature T c . But this result was in contradiction to the increase of the spin-relaxation rate with increasing temperature near T c from below in superconducting Nb films and potassium-doped fulleride (K 3 C 60 ) compounds measured by the electron spin resonance technique.20,21 More recent theoretical studies by Yamashita et al, 22 however, indicated that the estimated spin-diffusion length in both the superconducting state (neglecting the charge imbalance effect) and the normal-metallic state should be the same, implying that the spin-diffusion characteristics should be independent of temperature in the narrow temperature range below T c .On the other hand, studies on the influence of the spin-polarized quasiparticle injection into high-T c cuprates 25,26,27,28 have mainly been focused on the effective suppression of the superconductivity. The sensitive dependence of the critical current on the spin injection in a low-carrier-density cuprate hybridized with a highly polarized colossal magnetoresistance material is expected to open a way to develop active three-terminal superconducting devices with a high current gain.…”

“…On the other hand, studies on the influence of the spin-polarized quasiparticle injection into high-T c cuprates 25,26,27,28 have mainly been focused on the effective suppression of the superconductivity. The sensitive dependence of the critical current on the spin injection in a low-carrier-density cuprate hybridized with a highly polarized colossal magnetoresistance material is expected to open a way to develop active three-terminal superconducting devices with a high current gain.…”

“…15,16,17,18 Observed spin relaxation rate using different techniques at room temperature, where the electron-phonon interaction predominates the spin-orbit scattering, reveals reasonable consistency, but it shows a wider spread at low temperatures around liquid helium temperature. It has been pointed out that 9 , as the impurity scattering predominates the spin-orbit scattering at low temperatures, the measured spin relaxation rates may depend on different measurement techniques which are sensitive to different impurity-induced spin-orbit scattering.Recently, the spin relaxation in a superconductor (S), both conventional 19,20,21,22,23,24 and high-T c cuprate, 25,26,27,28 has attracted much research interest in relation with the recombination mechanism of the spin-polarized quasiparticles into the singlet Cooper-paired state. A number of studies on the spin diffusion in conventional superconductors, however, have revealed contradicting results.…”

“…Recently, the spin relaxation in a superconductor (S), both conventional 19,20,21,22,23,24 and high-T c cuprate, 25,26,27,28 has attracted much research interest in relation with the recombination mechanism of the spin-polarized quasiparticles into the singlet Cooper-paired state. A number of studies on the spin diffusion in conventional superconductors, however, have revealed contradicting results.…”

Pulsed Laser Deposition of Superconductor/Ferromagnetic YBa2Cu3Oy/SrTiO3/La2/3Sr1/3MnO3 Heterostructures

“…In addition, the tunneling effect is limited only to barriers thinner than 10 nm [1]. Sharp magnetic and electric interfaces between thin films are important in order to avoid scattering of spin polarized quasiparticles which can decrease efficiency of a spin injection device.…”