Spin-polarized quasiparticle transport in exchange-split superconducting aluminum on europium sulfide

We report on nonlocal spin transport in mesoscopic superconducting aluminum wires in contact with the ferromagnetic insulator europium sulfide. We find spin injection and long-range spin transport in the regime of the exchange splitting induced by europium sulfide. Our results demonstrate that spin transport in superconductors can be manipulated by ferromagnetic insulators, and opens a path to control spin currents in superconductors.

Figure 1

False-color scanning electron microscopy image of a section of one of our samples together with the measurement scheme with the injection (inj) and detection (det) circuits.

Figure 2

(a) Nonlocal resistance $R_{\mathrm{nl}}$ as a function of applied magnetic field $H$ for different contact separation $d$ in the normal state at $T=4.2$ K. The data are shifted vertically for clarity. (b) Spin-valve signal $\Delta R_{\mathrm{nl}}$ as a function of contact distance $d$ (symbols), and fit to an exponential decay (line).

Figure 3

(a) Local differential conductance $g_{\mathrm{loc}}=d{I}_{\mathrm{inj}}/d{V}_{\mathrm{inj}}$ of one junction as a function of injector bias $V_{\mathrm{inj}}$ for different applied magnetic fields $H$ (symbols) and fits (lines). Data are offset vertically for clarity. (b) Magnetization of the EuS film (solid line, left ordinate) and induced exchange field $B^{*}$ for different contacts (symbols, right ordinate) as a function of the applied field. (c) Pair potential $\Delta$ as a function of normalized field $H/H_{\mathrm{c}}$. (d) Normalized pair-breaking parameter $\Gamma /{\Delta }_0$ as a function of ${(H/H_{\mathrm{c}})}^2$.

Figure 4

Normalized nonlocal differential conductance ${\widehat{g}}_{\mathrm{nl}}=g_{\mathrm{nl}}/\left(G_{\mathrm{inj}}{G}_{\det }\right)$ as a function of injector bias $V_{\mathrm{inj}}$. (a) and (b) Data for different applied magnetic fields $H$ for one pair of contacts. (c) and (d) Data for different contact distances at two different applied fields.

Figure 5

(a) Normalized nonlocal differential conductance ${\widehat{g}}_{\mathrm{nl}}$ as a function of bias voltage $V_{\mathrm{inj}}$ for one contact pair and applied field (symbols) and theoretical prediction ${\widehat{g}}_{\mathrm{nl}}\propto g_{\downarrow }-g_{\uparrow }$ (line). (b) Relaxation length ${\lambda }_{\mathrm{S}}$ of the spin signal as a function of bias voltage $V_{\mathrm{inj}}$ for different magnetic fields $H$.