Spin-resolved Josephson diode effect through strongly spin-polarized conical magnets

We present a theoretical study of the spin-resolved Josephson diode effect in junctions comprising strongly spin-polarized conical magnets (FM) coupled to singlet superconductors (SC). The system is treated by making use of the Gor'kov and quasiclassical Green's function methods. Modeling the SC/FM interfaces as spin-dependent <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mi>δ</a:mi> </a:math> potentials, we apply our model to an SC/FM/SC junction and account for the Josephson current-phase relation (CPR). The nontrivial coupling between the spin bands in the conical magnet gives rise to a strong Josephson diode effect with an efficiency greater than <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mn>40</b:mn> <b:mo>%</b:mo> </b:mrow> </b:math> . The effect essentially depends on the quantum spin-geometric phase that enters the Josephson CPR in a very similar manner to the superconducting phase difference. The former is generated nonlocally by the intrinsically noncoplanar spin arrangement of the conical magnet, which breaks the time-reversal and inversion symmetries. Strong spin polarization and a helical pitch of the conical magnet comparable to the superconducting coherence length are essential for the effect. We perform a harmonic analysis of the Josephson CPR and interpret the effect in terms of coherent transfer of multiple equal-spin triplet Cooper pairs across the conical magnet.