Measuring the Spin Polarization of a Ferromagnet: an Application of Time-Reversal Invariant Topological Superconductor

The spin polarization (SP) of the ferromagnet (FM) is a quantity of fundamental importance in spintronics. In this work, we propose a quasi-one-dimensional junction structure composed of a FM and a time-reversal invariant topological superconductor (TRITS) with un-spin-polarized pairing type to determine the SP of the FM. We find that due to the topological property of the TRITS, the zero-bias conductance (ZBC) of the FM/TRITS junction which is directly related to the SP is a non-quantized but topological quantity. The ZBC only depends on the parameters of the FM, it is independent of the interface scattering potential and the Fermi surface mismatch between the FM and the superconductor, and is robust against to the magnetic proximity effect, therefore, compared to the traditional FM/$s$-wave superconductor junction, the topological property of the ZBC makes this setup a much more direct and simplified way to determine the SP.