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TT: Fachverband Tiefe Temperaturen

TT 55: Superconductivity: Tunnelling and Josephson Junctions

TT 55.4: Vortrag

Donnerstag, 19. März 2020, 10:30–10:45, HSZ 204

Coupling ferromagnetic insulators via quasiparticle states in a nodal superconductor — •Angelo Di Bernardo^1,2, Sachio Komori², Giorgio Livanas³, Giorgio Divitini², Paola Gentile³, Mario Cuoco³, and Jason Robinson² — ¹Universität Konstanz, Department of Physics, Universitätsstraße 10, Konstanz, Germany — ²Universitatstrasse 10 — ³CNR-SPIN, c/o University of Salerno, I-84084 Fisciano, Salerno, Italy

The generation of parallel-aligned spin (spin-triplet) pairs of electrons at superconductor/ferromagnet (S/F) interfaces has triggered the field of superconducting spintronics –which aims at developing spintronic devices with high energy efficiency.

Even before the discovery of giant magneto resistance, which underlies spintronic spin valves, de Gennes predicted a FI/S/FI system (FI is a ferromagnetic insulator), where a variation in the critical temperature (Δ T_c) of S can be obtained by switching the FIs from parallel (P) to antiparallel (AP). In addition, if the S thickness (d_S) is smaller than its coherence length (ξ), S can favour an AP coupling of the FIs.

Recently, we have investigated a fully-oxide FI/S/FI system [1], where FI is the manganite Pr_0.8Ca_0.2MnO₃ and S is the nodal (d-wave) S YBa₂Cu₃O_7−δ (YBCO). Here, quasiparticle states at the Fermi surface of YBCO, induce a long-ranged exchange coupling between the FIs over a d_S up to 100 ξ, which is well-beyond de Gennes limit for a metallic FI/S/FI system. Such nodal exchange coupling reinforces an AP state at specific d_S and results in Δ T_c values up to 2 K.

[1] A. Di Bernardo et al., Nature Mater. 18, 1194 (2019).