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

Abstract

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 new path to control spin currents in superconductors.

Long-Range Spin Accumulation from Heat Injection in Mesoscopic Superconductors with Zeeman Splitting

“…This may correspond to the case of a Zeeman field caused by the proximity of a ferromagnetic insulator [11]. Figure 2d shows a clearly different behavior for g nl (V inj ) with respect to the large α orb case, and can be observed in the experiments [11].…”

“…This estimation yields α orb = 1.33 for the film width W = 8 nm. The Zeeman field can also be induced by an exchange field in a FS proximity system [11]. In this case τ orb is not directly related to the Zeeman field and we describe this with α orb = 0 in the numerical results below.…”

“…For example, in Al wires used in the spin-transport experiments, the typical spin relaxation time is τ Σ ≈ 800 ps ≈ 40/T c where T c ≈ 1.6 K. For the spin accumulation experiments [7,8,11] the value of β can be inferred from the magnetic depairing parameter ζ = 8 · 10 −4 in the absence of a magnetic field. It is proportional to the spin-flip scattering rate ζ = 3(1 + β)/(2τ Σ T c ) which yields β ≈ −0.98.…”

“…Second, the non-local conductance g nl depends drastically on the origin of the Zeeman splitting. Such a splitting can be caused either by an applied (strong) external magnetic field [6,7] or by the proximity of a ferromagnetic insulator [11].…”

“…Second, the non-local conductance g nl depends drastically on the origin of the Zeeman splitting. Such a splitting can be caused either by an applied (strong) external magnetic field [6,7] or by the proximity of a ferromagnetic insulator [11].In this Letter, we develop a microscopic model based on the well-established Keldysh kinetic equations for superconductors extended to spin-dependent phenomena, and solve this puzzle. In particular we show that: (i) The observed long-range spin accumulation can be understood as a thermoelectric effect for Bogoliubov quasiparticles.…”