Supercurrent in ferromagnetic Josephson junctions with heavy metal interlayers

Abstract

The lengthscale over which supercurrent from conventional BCS, s-wave, superconductors (S ) can penetrate an adjacent ferromagnetic (F ) layer depends on the ability to convert singlet Cooper pairs into triplet Cooper pairs. Spin aligned triplet Cooper pairs are not dephased by the ferromagnetic exchange interaction, and can thus penetrate an F layer over much longer distances than singlet Cooper pairs. These triplet Cooper pairs carry a dissipationless spin current and are the fundamental building block for the fledgling field of superspintronics. Singlet-triplet conversion by inhomogeneous magnetism is well established. Here, we describe an attempt to use spin-orbit coupling as a new mechanism to mediate singlet-triplet conversion in S-F-S Josephson junctions.We report that the addition of thin Pt spin-orbit coupling layers in our Josephson junctions significantly increases supercurrent transmission, however the decay length of the supercurrent is not found to increase. We attribute the increased supercurrent transmission to Pt acting as a buffer layer to improve the growth of the Co F

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

“…Therefore, it would be desirable to identify a setup where the LRTs can be tuned with a sole in-plane variation of the magnetization to minimize the stray field effect on the superconductor itself. This would be a different result than previous works [13,14,[16][17][18][19][20] that have considered how to control the supercurrent via magnetization in Josephson contacts with spin-orbit coupling. A long-ranged supercurrent was predicted in Ref.…”

“…The long-ranged component will be component that is perpendicular to the exchange field d LRC = |d × M | while the short-ranged component is parallel to the exchange field d SRC = d·M . We can now enter our d-vector into equation (14). The set of Pauli matrices with the addition of the identity matrices form a basis for a general 2×2 matrix.…”

“…Very recently, Ref. [14] did not find any clear signature of a long-ranged triplet supercurrent in a Josephson junction including heavy metals and multilayers of ferromagnets with an effective canted magnetization direction. Therefore, it would be desirable to identify a setup where the LRTs can be tuned with a sole in-plane variation of the magnetization to minimize the stray field effect on the superconductor itself.…”

“…[12] that in S/F bilayers with Rashba spin-orbit coupling, the magnetization requires an out-of-plane component to generate the LRT. Although such a scenario is possible to obtain experimentally [13][14][15], it complicates the unambiguous identification of spin-polarized Cooper pairs due to the additional flux injection from domain walls from the ferromagnet and also severely restricts the choice of materials showing a tailored out-of-plane anisotropy. Very recently, Ref.…”

Origin of superconductivity at nickel-bismuth interfaces

“…It is also possible to generate spin-triplet states in proximity coupled thin films where s-wave pairing is retained by introducing a Berizinskii state with spontaneous breaking of time-reversal symmetry [33]. Our Bi/Ni samples contain all the necessary ingredients for such a state to occur; a source of s-wave superconductivity (NiBi 3 ), ferromagnetism (Ni) and strong spin-orbit coupling (Bi) [34][35][36][37].…”