Electron transport in hybrid superconductor heterostructures with manganite interlayers

摘要

Hybrid herostructures comprising an YBa_2Cu_3O _x (YBCO) high-temperature superconductor (HTS) layer and Nb/Au low-temperature superconductor (LTS) bilayer (with critical HTS and LTS temperatures T c and T′c, respectively), separated by a thin (d _M = 5-20 nm) interlayer of LaMnO_3, La _(0.7)Ca_(0.3)MnO_3, or La_(0.7)Sr _(0.3)MnO_3 manganite have been studied. The electric resistance and magnetic properties of individual (evaporated directly onto the substrate) manganite films and related hybrid herostructures have been measured. Based on quasi-classical equations, analytical expressions for the conductivity of herostructures at T ≥ T′_c are obtained in the case of a low-transparency superconductor/manganite interface. It is established that the conductivity of heterostructures is determined by the proximity effect (related to the penetration of a condensate wavefunction from the Nb/Au bilayer to manganite) and depends strongly on interface transparency. At low temperatures (T ? T _c′), the conductivity peaks are found at voltages determined by the exchange field of the manganite interlayer. At T _c′ < T < T _c, conductivity features at nearly zero bias voltages are observed, which are related to the superconductivity of the YBCO electrode.