Spin supercurrent in Josephson contacts with noncollinear ferromagnets

Abstract

We present a theoretical study of the Josephson coupling of two superconductors which are connected through a diffusive contact consisting of noncollinear ferromagnetic domains. The leads are conventional s-wave superconductors with a phase difference of ϕ. First, we consider a contact with two domains with magnetization vectors misoriented by an angle θ. Using the quantum circuit theory, we find that in addition to the charge supercurrent, which shows a 0−π transition relative to the angle θ, a spin supercurrent with a spin polarization normal to the magnetization vectors flows between the domains. While the charge supercurrent, is odd in ϕ and even in θ, the spin supercurrent is even in ϕ and odd in θ. Furthermore, with asymmetric insulating barriers at the interfaces of the junction, the system may experience an antiferromagnetic-ferromagnetic phase transition for ϕ = π. Secondly, we discuss the spin supercurrent in an extended magnetic texture with multiple domainwalls. We find the position-dependent spin supercurrent. While the direction of the spin supercurrent is always perpendicular to the plane of the magnetization vectors, the magnitude of the spin supercurrent strongly depends on the phase difference between the superconductors and the number of domain walls. In particular, our results reveal a high sensitivity of the spin-and charge-transport in the junction to the number of domain walls in the ferromagnet. We show that superconductivity in coexistence with non-collinear magnetism, can be used in a Josephson nanodevice to create a controllable spin supercurrent acting as a spin transfer torque on a system. Our results demonstrate the possibility to couple the superconducting phase to the magnetization dynamics and, hence, constitutes a quantum interface e.g. between the magnetization and a superconducting qubit. Spin supercurrent inJosephson contacts with noncollinear ferromagnets 2 (b) x=0 (a) θ S 2 S 1

Unconventional superconductivity in double quantum dots

“…For noncollinear magnetizations, e.g., due to domain walls [11][12][13][14][15][16][17], spin-active interfaces [18,19], multiple noncollinear magnetized ferromagnetic layers [17,20,21], helical magnets [22][23][24], or spin-orbit coupling [25], odd-frequency correlations with finite spin polarization can penetrate deeply into ferromagnets, as confirmed in several experiments [26][27][28][29][30][31][32].…”

“…By a similar mechanism, Majorana fermions can also be generated in double quantum dots [7,8]. The idea of odd-frequency pairing has first been brought up by Berezinskii [9] as a possible explanation of superfluid 3 He but has experienced a revival in the context of superconductor-ferromagnet heterostructures [10].For noncollinear magnetizations, e.g., due to domain walls [11][12][13][14][15][16][17], spin-active interfaces [18,19], multiple noncollinear magnetized ferromagnetic layers [17,20,21], helical magnets [22][23][24], or spin-orbit coupling [25], odd-frequency correlations with finite spin polarization can penetrate deeply into ferromagnets, as confirmed in several experiments [26][27][28][29][30][31][32].Odd-frequency triplet pairing also appears in diffusive normal metals contacted by an even-frequency triplet superconductor [33].Finally, odd-frequency singlet superconductivity has only been theoretically predicted [34] without experimental confirmation so far. Quantum dots coupled to conventional superconductors show an interesting interplay of proximity effect and Coulomb interaction [35,36].…”

A spin triplet supercurrent in half metal ferromagnet/superconductor junctions with the interfacial Rashba spin-orbit coupling

“…As discussed in Ref. 30, in our systems there exists a spin polarized supercurrent directed normal to h, which is proportional to the induced spin-transfer torque acting on the local magnetization of the HMF, so our systems also can be useful for designing the spin-transfer torque device.…”

Theoretical Study of Magnetism Induced by Proximity Effect in a Ferromagnetic Josephson Junction with a Normal Metal

“…[59][60][61] As well as the detection of STC by measuring the Josephson critical current and T C as mentioned above, the spin-dependent transport of STC in S/F hybrid junctions gives a direct evidence of spin in the STC . 22,29,[62][63][64][65][66][67][68] One of the simplest quantity induced by the spin of the STC is a magnetization induced by the proximity effect of STC . 22,29,62,65,67) In F/S junctions, the STC is also induced to S by the inverse proximity effect.…”