Strongly spin-polarized current generated in a Zeeman-split unconventional superconductor

We consider a thin-film normal-metal/superconductor junction in the presence of an externally applied in-plane magnetic field for several symmetries of the superconducting order parameter. For $p$-wave superconductors, a strongly spin-polarized current emerges due to an interplay between the nodal structure of the superconducting order parameter, the existence or nonexistence of zero-energy surface states, and the Zeeman splitting of the bands which form superconductivity. Thus, the polarization depends strongly on the orbital symmetry of the superconducting state. Our findings suggest a mechanism for obtaining fully spin-polarized currents crucially involving zero-energy surface states, not present in $s$-wave superconductors.

Figure 1

(Color online) Plot of the spin polarization of the tunneling current for an $s$-wave symmetry. In the right panels, the full-drawn (dashed) line corresponds to majority (minority) spin.

Figure 2

(Color online) Plot of the spin polarization of the tunneling current for a chiral $p$-wave symmetry. In the right panels, the full-drawn (dashed) line corresponds to majority (minority) spin.

Figure 3

(Color online) Plot of the spin-polarization of the tunneling current for a $p_x$-wave symmetry. In the right panels, the full-drawn (dashed) line corresponds to majority (minority) spin.

Figure 4

(Color online) Comparing the $s$-wave and the $p_x$-wave symmetries for different exchange fields at $Z=50$.

Figure 5

(Color online) The experimental setup proposed in this paper. In (a), an in-plane magnetic field is applied to the junction. In (b), an exchange field is induced by a ferromagnetic film in close proximity. We will consider three different symmetries of the superconducting state, as shown above. In the chiral $p$-wave case, the gap has an intrinsic complex angular dependence and a constant magnitude. The system we consider is similar to that of Ref. 14.