Spin-polarized Cooper pairs in unconventional magnets

Sammanfattning

We investigate the emergence of spin-polarized Cooper pairs by combining unconventional magnetism and conventional superconductivity. In particular, d-wave and p-wave unconventional magnets and spin singlet s-wave superconductivity. We characterize the pairing correlations using the electron-hole Green’s function and identify their symmetries under Fermi-Dirac statistics. We find that, while conventional superconductors creates spin singlet s-wave Cooper pairs, unconventional magnetism enables the formation of spin triplet Cooper pairs along the z-axis whereelectrons posses mixed spins in both d- and p-wave magnets. While both types of unconventional magnets lead to mixed spin triplet Cooper pairs, the parity and frequency dependence aredifferent for each case. For d-wave altermagnets, the spin triplet Cooper pairs appear with an odd-frequency behavior and d-wave parity, while for p-wave magnets they develop an even-frequency and p-wave parity. Moreover, we also explore the impact of Rashba spin-orbit coupling on a system with both unconventional magnets and conventional superconductivity. In this case, we show that spin-orbit coupling leads to Cooper pairs where electrons have the same spins. Specifically, we discover that the unique interplay of spin-orbit coupling and d-wave altermagnetism leads to equal spin Cooper pairs along the y-direction, that does not exist without d-wave altermagnetism. These findings uncover a promising route to engineer spin-polarized Cooper pairs, which canfurther help advancing the field of superconducting spintronics without external magnetism.