Non-local conductance in three-terminal Majorana nanowires part 2 - spin-polarization of the bulk bands

High spin-orbit semiconducting nanowires coupled to superconductors are predicted to undergo a topological phase transition at a finite magnetic field, accompanied by the appearance of Majorana zero modes. At the phase transition, the superconducting gap at the low momentum region of the Brillouin zone is closed and is re-opened due to the Zeeman term. The low energy excitations of the bulk nanowire bands are thus expected to be spin-polarized, and this polarization is expected to flip sign across the phase transition. Using non-local conductance measurements that include spin-polarized quantum dots, we measure the spin polarization of the bulk bands. With the application of small magnetic fields, we observe trivial spin polarization signatures that disappear following the closing of the induced gap. We discuss the implication of these results to the attempts of achieving topological superconductivity in porximitized nanowires.