Critical temperature of triplet superconductor-ferromagnet bilayers as a probe for pairing symmetry

Abstract

Identifying superconducting materials with spin-polarized Cooper pairs is an important objective both for exploration of new fundamental physics and for cryogenic applications in spintronics and quantum sensing. We here compute the critical temperature Tc of the superconducting transition in a bilayer composed of a superconductor with an intrinsic spin-triplet order parameter and a ferromagnet. We determine how Tc varies both with the thickness of the ferromagnet and its magnetization direction. We show that both the orbital and spin part of the triplet superconducting order parameter leave clear signatures in Tc which do not appear in a bilayer of a conventional s-wave superconductor and a ferromagnet. In particular, the dependence of Tc on these variables changes depending on whether or not the superconducting order parameter features Andreev bound states and also changes qualitatively when the magnetization is rotated in the plane of the ferromagnetic film. We also show that a single-component triplet order parameter, such as py-wave, can have a strong enhancement near a boundary due to the Friedel oscillations causing an energy-dependent modulation of the local density of states. Measurements of Tc in such bilayers are therefore useful to identify the pairing symmetry of intrinsic triplet superconductors.

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