We study numerically the properties of spin-and charge-transport in a current-biased nanoscale diffusive superconductor|ferromagnet|superconductor junction when the magnetization texture is non-uniform. Specifically, we incorporate the presence of a Bloch/Neel domain walls and conical ferromagnetism, including the role of spin-active interfaces. The superconducting leads are assumed to be of the conventional s-wave type. In particular, we investigate how the 0-π transition is influenced by the inhomogeneous magnetization texture and focus on the particular case where the charge-current vanishes while the spin-current is non-zero. In the case of a Bloch/Neel domain-wall, the spin-current can be seen only for one component of the spin polarization, whereas in the case of conical ferromagnetism the spin-current has the three components. This is in contrast to a scenario with a homogeneous exchange field, where the spin-current vanishes completely. We explain all of these results in terms of the interplay between the triplet anomalous Green's function induced in the ferromagnetic region and the local direction of the magnetization vector in the ferromagnet. Interestingly, we find that the spin-current exhibits discontinuous jumps at the 0-π transition points of the critical charge-current. This is seen both in the presence of a domain wall and for conical ferromagnetism. We explain this result in terms of the different symmetry obeyed by the current-phase relation when comparing the charge-and spin-current. Specifically, we find that whereas the charge-current obeys the well-known relation Ic(φ) = −Ic(2π − φ), the spin-current satisfies Is(φ) = Is(2π − φ), where φ is the superconducting phase difference.
The influence of electron reflection on dc Josephson effect in a ballistic point contact with transport current in the banks is considered theoretically. The effect of finite transparency on the vortex-like currents near the contact and at the phase difference φ = π, which has been predicted recently 1 , is investigated. We show that at low temperatures even a small reflection on the contact destroys the mentioned vortex-like current states, which can be restored by increasing of the temperature.
We present an investigation of heat transport in gapless graphene-based Ferromagnetic /singlet Superconductor/Ferromagnetic (FG|SG|FG) junctions. We find that unlike uniform increase of thermal conductance vs temperature, the thermal conductance exhibits intensive oscillatory behavior vs width of the sandwiched s-wave superconducting region between the two ferromagnetic layers. This oscillatory form is occurred by interference of the massless Dirac fermions in graphene. Also we find that the thermal conductance vs exchange field h displays a minimal value at h/E F 1 within the low temperature regime where this finding demonstrates that propagating modes of the Dirac fermions in this value reach at their minimum numbers and verifies the previous results for electronic conductance. We find that for thin widths of superconducting region, the thermal conductance vs temperature shows linear increment i.e. Γ ∝ T . At last we propose an experimental set-up to detect our predicted effects.
We study the tunneling magneto-transport properties of the Ferromagnetic Insulator-Normal Insulator-Ferromagnetic Insulator(F|N|F) and Ferromagnetic Insulator-Barrier Insulator-Ferromagnetic Insulator (F|B|F) junctions on the surface of topological insulator in which in-plane magnetization directions of both ferromagnetic sides can be parallel and antiparallel. We derive analytical expressions for electronic conductances of the two mentioned junctions with both parallel and antiparallel directions of magnetization and using them calculate magnetoresistance of the two junctions. We use thin barrier approximation for investigating the F|B|F junction. We find that although magnetoresistance of the F|N|F and F|B|F junctions are tunable by changing the strength of magnetization texture, they show different behaviors with variation of magnetization. In contrast to the magnetoresistance of F|N|F, magnetoresistance of F|B|F junctions shows very smooth enhance by increasing the strength of magnetization. We suggest an experimental set up to detect our predicted effects.
The spin current in the Josephson junction as a weak-link (interface) between misorientated triplet superconductors is investigated theoretically for the models of the order parameter in U P t3. Green functions of the system are obtained from the quasiclassiacl Eilenberger equations. The analytical results for the charge and spin currents are illustrated by numerical calculations for the certain misorientation angles of gap vector of superconductors. As the main result of this paper, it is found that, at some values of the phase difference, at which the charge current is exactly zero, the spin current has its maximum value. Furthermore, it is shown that the origin of spin current is the misorientation between gap vectors of triplet superconductors.
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