Phys. Rev. B 101, 020502(R) (2020)
Spin-polarized multiple Andreev reflections in spin-split superconductors
Bo Lu1, Pablo Burset2, and Yukio Tanaka3
1 Center for Joint Quantum Studies and Department of Physics, Tianjin University, Tianjin 300072, China
2 Department of Applied Physics, Aalto University, 00076 Aalto, Finland
3 Department of Applied Physics, Nagoya University, Nagoya 464-8603, Japan
We study the transport properties of a voltage-biased contact between two spin-split superconductors separated by an insulating barrier of arbitrary transparency. At low transparency, the contribution of multiple Andreev reflections leads to a subharmonic gap structure that crucially depends on the amplitude and relative angle of the spin-splitting fields of each superconductor. For noncollinear fields, we find an interesting even-odd effect on the bound states within the gap, where the odd order multiple Andreev reflections split, but the even order ones remain at their expected positions. By computing the current-voltage characteristics, we determine the transparency required for the emergence of a subharmonic gap structure and show that the splitting of the odd bound states is associated with different threshold energies of spin-polarized Andreev processes. Our findings provide a tool to experimentally determine the amplitude and alignment of Zeeman fields in spin-split superconductors.