Long-ranged triplet supercurrent in a single in-plane ferromagnet with spin-orbit coupled contacts to superconductors

Abstract

By converting conventional spin-singlet Cooper pairs to polarized spin-triplet pairs, it is possible to sustain long-ranged spin-polarized supercurrents flowing through strongly polarized ferromagnets. Obtaining such a conversion via spin-orbit interactions, rather than magnetic inhomogeneities, has recently been explored in the literature. A challenging aspect with regard to experimental detection has been that in order for Rashba spinorbit interactions, present e.g. at interfaces due to inversion symmetry breaking, to generate such long-ranged supercurrents, an out-of-plane component of the magnetization is required. This limits the choice of materials and can induce vortices in the superconducting region complicating the interpretation of measurements. Therefore, it would be desirable to identify a way in which Rashba spin-orbit interactions can induce long-ranged supercurrents for purely in-plane rotations of the magnetization. Here, we show that this is possible in a lateral Josephson junction where two superconducting electrodes are placed in contact with a ferromagnetic film via two thin, heavy normal metals. The magnitude of the supercurrent in such a setup becomes tunable by the in-plane magnetization angle when using only a single magnetic layer. These results could provide a new and simpler way to generate controllable spin-polarized supercurrents than previous experiments which utilized complicated magnetically textured Josephson junctions. arXiv:1906.07725v1 [cond-mat.supr-con]

Odd triplet superconductivity induced by a moving condensate

“…The described mechanism has the same physical origin as the one reported in Ref. [98], where the gradients of pairing amplitude arising near the edges of S and Pt layers in the planar geometry in combination with Rashba SOC can generate LRTs. In our proposal LRTs are generated within the entire Pt layers thus providing much larger long-range Josephson currents.…”

“…For the superconducting gap in Nb ∼ 10 K so that the critical current is I c ∼ 10 −1 (p s ξ ) 2α2 A. Takingα ∼ 0.1-1 [27,89,112] and p s ξ = 0.3, we get the current I c ∼ 10 −2 -10 −4 A which is much larger than in SFS junctions where LRTs are generated by the magnetic inhomogeneity [49]. This I c is much larger than obtained for the planar geometry [98] because in our mechanism there are no physical limitations on the junction cross section.…”

“…This shows up in the generation of LRT pairs which are robust to both disorder and exchange interaction. This effect can be engineered combining usual superconductors such as Al or Nb with ferromagnets and SOC [70][71][72]75,86,[97][98][99].…”

Boosting spintronics with superconductivity

“…Another theoretical and subsequent experimental work demonstrated that the superconducting condensation energy can induce the magnetic reorientation in a ISOC-present SC/FM heterostructure. 75,76 We also note that vertical heterostructures with in-plane magnetization and ISOC interaction have been experimentally explored, but LRTC due to ISOC have not been observed. 77,78 Based on previous theoretical works, 73 the conditions for the generation of LRTC by SOC are quite restrictive in vertical structures, more favourable layouts are involving lateral structures where supercurrents have a component flowing in the direction parallel to the hybrid interfaces.…”

Superconducting triplet rim currents in a spin-textured ferromagnetic disk

“…[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. 47,48 However, the experimental evidence to verify such models remains scarce.…”