Nonequilibrium superconductivity under spin-polarized quasiparticle currents in perovskite ferromagnet-insulator-superconductor heterostructures

Abstract

We report phenomena manifesting nonequilibrium superconductivity induced by spin-polarized quasiparticles in perovskite ferromagnet-insulator-superconductor ͑F-I-S͒ heterostructures. Measurements of the critical current J c , using a pulsed current technique to minimize Joule heating, reveal a monotonic increase with increasing insulator thickness; and for F-IS with thin insulating barriers, a slight increase in J c is observed under small injection currents I m from the ferromagnet, followed by a strong suppression of J c under large I m. In contrast, no effect of injection on J c can be detected in the N-IS control sample ͑N: nonmagnetic metal͒. The spin diffusion time and length in cuprate superconductors are also estimated and compared with our experimental results. ͓S0163-1829͑99͒05638-6͔

Spin diffusion versus proximity effect at ferromagnet/superconductorLa0.7Ca0.3MnO3∕YBa2Cu3OPeña1, Visani2, García‐Barriocanal3 et al. 2006Phys. Rev. B541251View full textAdd to dashboardCite

“…S can be estimated by the relation S ϳ 3.7ប k B T c / E ex ⌬͑T͒, where E ex ϳ30 K is the average on-site spin exchange interaction in YBCO and ⌬͑T͒ = ⌬͑0͒͑1−T / T c ͒ 0.5 is the temperaturedependent gap. Assuming a value of S =10 −13 s, 41 v F =10 7 cm/ s and that the electron mean free path of YBCO is l 0 = 20 nm, l S can be of the order of 14 nm, in agreement with the 10 nm estimated recently by Soltan et al 43 This work also reports on LCMO/YBCO bilayers although focusing on much thicker YBCO layer thickness.…”

“…LCMO is a relatively bad metal and many collision events will result in electrons being scattered into the YBCO. These electrons will be highly spin polarized and are expected to cause T c depression by pair breaking as previously discussed by other authors [40][41][42] if the YBCO thickness is smaller than the spin diffusion length, l S . An estimate of l S in YBCO can be obtained using the relation l S = ͑l 0 v F S ͒ 0.5 , 41 where S is the spin-polarized quasiparticle diffusion time, v F is the Fermi velocity, and l 0 is the electron mean free path.…”

“…These electrons will be highly spin polarized and are expected to cause T c depression by pair breaking as previously discussed by other authors [40][41][42] if the YBCO thickness is smaller than the spin diffusion length, l S . An estimate of l S in YBCO can be obtained using the relation l S = ͑l 0 v F S ͒ 0.5 , 41 where S is the spin-polarized quasiparticle diffusion time, v F is the Fermi velocity, and l 0 is the electron mean free path. S can be estimated by the relation S ϳ 3.7ប k B T c / E ex ⌬͑T͒, where E ex ϳ30 K is the average on-site spin exchange interaction in YBCO and ⌬͑T͒ = ⌬͑0͒͑1−T / T c ͒ 0.5 is the temperaturedependent gap.…”

Proximity effect, quasiparticle transport, and local magnetic moment in ferromagnet–d-wave-superconductor junctions

“…In an earlier theoretical work, 5 this effect was studied in the zero-bias limit. Several recent spin injection experiments [6][7][8][9] have been done with high-T c superconductors. Common to both ferromagnetconventional and high-T c superconductor junctions, the subgap conductance at a given bias is suppressed due to the suppression of AR by the spin splitting of energy band in the ferromagnet.…”

Superconducting and normal-state interlayer exchange coupling inLa0.67Sr0.33MnO3−YSenapati1, Budhani2 2005Phys. Rev. B360350View full textAdd to dashboardCite

“…Reported measurements on high T c superconductor (HTSC)-manganite heterostructures have primarily focused on the suppression of T c 12,13,14 , spin injection 15,16,17 and the effects on magnetoresistance 18,19 . Recently, the aspect of exchange coupling across HTSC layers has been addressed by Przyslupski et al 20 using (La 0.67 Sr 0.33 MnO 3 ) n /(YBa 2 Cu 3 O 7 ) m multilayers where n = 16 unit cells, and m varies from 1 to 8 unit cells.…”