Influence of the Fermi surface geometry on the Josephson effect between iron-pnictide and conventional superconductors
A. A. Kalenyuk, E. A. Borodianskyi, A. A. Kordyuk, V. M. Krasnov
Abstract
We study hybrid Josephson junctions between a multiband ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Na}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ iron-pnictide and Nb. We observe that the insertion of a Cu interlayer in such junctions leads to a dramatic enhancement of the ${I}_{c}{R}_{n}$ product, despite the weaker proximity-induced superconductivity of Cu. This counterintuitive phenomenon is attributed to the differences in Fermi surface geometries of Nb and Cu, which affect the selectivity of tunneling in sign-reversal ${s}_{\ifmmode\pm\else\textpm\fi{}}$ bands of pnictide. Our results indicate that the sensitivity to Fermi surface geometries provides a new tool for phase-sensitive studies and paves the way to conscious Fermi surface engineering of pnictide junctions.