Nodal superconducting exchange coupling

A superconducting spin valve consists of a thin-film superconductor between two ferromagnetic layers. A change of magnetization alignment shifts the superconducting transition temperature (Δ Τ c ) due to an interplay between the magnetic exchange energy and the superconducting condensate. The magnitude of Δ Τ c scales inversely with the superconductor thickness ( d S ) and is zero when d S exceeds the superconducting coherence length ( ξ ). Here, we report a superconducting spin-valve effect involving a different underlying mechanism in which magnetization alignment and Δ Τ c are determined by nodal quasiparticle excitation states on the Fermi surface of the d -wave superconductor YBa 2 Cu 3 O 7– δ sandwiched between insulating layers of ferromagnetic Pr 0.8 Ca 0.2 MnO 3 . We observe Δ Τ c values that approach 2 K with the sign of Δ Τ c oscillating with d S over a length scale exceeding 100 ξ and, for particular values of d S , the superconducting state reinforces an antiparallel magnetization alignment. These results pave the way to all-oxide superconducting memory in which superconductivity modulates the magnetic state. A d -wave superconductor is used to mediate a long-range exchange coupling between two ferromagnetic insulators.