Spin-polarized quasiparticles injection in La0.7Sr0.3MnO3∕SrTiO3∕Nb heterostructure devices

We report the effect of spin-polarized quasiparticle injection from a ferromagnetic manganite into a conventional Nb superconductor in a La0.7Sr0.3MnO3∕SrTiO3∕Nb heterostructure. A 8-terminal stacked trilayer geometry was used, where the injected current Iinj enters a superconducting microbridge and leaves it symmetrically by tunneling through a SrTiO3 barrier. A high dynamic gain G=−dIc∕dIinj was observed from 1.7 up to 8.5K, where Ic is the microbridge critical current. For a dc injection current, G was measured to be 290 at 1.7K. A SrTiO3 barrier of thickness in the range 3.5–8.5nm was found to provide a suitable spin injection length of the order of the bridge length and a low Joule heating level. In this confined stacked device geometry it was found that Joule dissipation in the manganite and barrier does not contribute significantly to the suppression of Ic, in contrast with previous studies.