Magnetization Control and Transfer of Spin-Polarized Cooper Pairs into a Half-Metal Manganite

Abstract

The pairing state and critical temperature (Tc) of a thin s-wave superconductor (S) on two or more ferromagnets (F) are controllable through the magnetization-alignment of the F layers. Magnetization misalignment can lead to spin-polarized triplet pair creation, and since such triplets are compatible with spin-polarized materials they are able to pass deeply into the F layers and so, cause a decrease in Tc. Various experiments on S/F1/F2 "triplet spin-valves" have been performed with the most pronounced suppression of Tc reported in devices containing the half-metal ferromagnet (HMF) CrO2 (F2) albeit using out-of-plane magnetic fields to tune magnetic non-collinearity [Singh et al., Phys. Rev. X 5, 021019 (2015)]. Routine transfer of spin-polarized triplets to HMFs is a major goal for superconducting spintronics so as to maximize triplet-state spin-polarization. However, CrO2 is chemically unstable and out-of-plane fields are undesirable for superconductivity. Here, we demonstrate magnetization-tuneable pair conversion and transfer of spin-polarized triplet pairs to the chemically stable mixed valence manganite La2/3Ca1/3MnO3 in a pseudo spin-valve device using in-plane magnetic fields. The results match microscopic theory and offer full control over the pairing state.