Spin-orbit coupling suppression and singlet-state blocking of spin-triplet Cooper pairs

Abstract

An inhomogeneous magnetic exchange field at a superconductor/ferromagnet interface converts spin-singlet Cooper pairs to a spin-polarized triplet state. Although the decay envelope of triplet pairs within ferromagnetic materials is well studied, little is known about their decay in nonmagnetic metals and superconductors and, in particular, in the presence of spin-orbit coupling (SOC). Here, we investigate devices in which singlet and triplet supercurrents propagate into the s-wave superconductor Nb. In the normal state of Nb, triplet supercurrents decay over a distance of 5 nm, which is an order of magnitude smaller than the decay of spin-singlet pairs due to the SOC. In the superconducting state of Nb, triplet supercurrents are not able to couple with the singlet wave function and are thus blocked by the absence of available equilibrium states in the singlet gap. The results offer insight into the dynamics between s-wave singlet and s-wave triplet states.

Boosting spintronics with superconductivity

“…Our recent work shows a strong suppression of triplet supercurrents in the normal and superconducting states of Nb due to the enhanced spin scattering and lack of available equilibrium states, respectively. 97 Therefore, proper stack materials should be selected in spin triplet devices to ensure good spin-transfer efficiency.…”

A Review of Electronic Transport in Superconducting Sr2RuO4 Junctions

“…Such pwave superconductivity offers spin and orbital degrees of freedom. We note that spintriplet Cooper pairs with odd-parity s-wave symmetry can be generated at an interface between an s-wave superconductor (SC) and a ferromagnet (F) [3,4]-for example, spinmixing due to the ferromagnetic exchange field generates m = 0 spin-triplet Cooper pairs, and broken spin-rotational symmetry converts m = 0 triplets into equal spin m = ±1 triplet pairs [5][6][7][8][9][10][11][12][13][14]. Moreover, broken inversion symmetry at an SC/F interface generates spin-orbit coupling (SOC), which creates interfacial spin-triplet superconductivity [15][16][17].…”

Superconducting triplet rim currents in a spin-textured ferromagnetic disk

“…19,20 However, the controlled generation of LRT currents has proven to be a demanding process, commonly realized in complex superconductor-ferromagnet (S-F) hybrids, involving multiple F layers with non-collinear magnetization. [21][22][23][24][25][26][27][28][29][30][31][32][33][34] Signatures of long-range proximity have also been reported for ferromagnetic Josephson junctions containing a heavy metal. [35][36][37][38][39][40][41] In parallel, a substantial body of theoretical studies have considered the possibility of generating and controlling LRT correlations using spin-textured systems, such as domain walls [42][43][44][45][46] and vortices.…”