arXiv subjects

Mohammad Alidoust

Publications and source records attributed to Mohammad Alidoust.

57 records · Page 4Linked to original sources

arXiv2010

Spin-triplet Supercurrent through Inhomogeneous Ferromagnetic Trilayers

Motivated by a recent experiment [J. W. A. Robinson, J. D. S. Witt and M. G. Blamire, Science, \textbf{329}, 5987 (2010)], we here study the possibility of establishing a long-range spin-triplet supercurrent through an inhomogeneous ferromagnetic region consisting of a Ho$\mid$Co$\mid$Ho trilayer sandwiched between two conventional s-wave superconductors. We utilize a full numerical solution in the diffusive regime of transport and study the behavior of the supercurrent for various experimentally relevant configurations of the ferromagnetic trilayer. We obtain qualitatively very good agreement with experimental data regarding the behavior of the supercurrent as a function of the width of the Co-layer, $L_\text{Co}$. Moreover, we find a synthesis of 0-$π$ oscillations with superimposed rapid oscillations when varying the width of the Ho-layer which pertain specifically to the spiral magnetization texture in Ho. We are not able to reproduce the anomalous peaks in the supercurrent observed experimentally in this regime, but note that the results obtained are quite sensitive to the exact magnetization profile in the Ho-layers, which could be the reason for the discrepancy between our model and the experimental reported data for this particular aspect. We also investigate the supercurrent in a system where the intrinsically inhomogeneous Ho ferromagnets are replaced with domain-wall ferromagnets, and find similar behavior as in the Ho$\mid$Co$\mid$Ho case. Furthermore, we propose a novel type of magnetic Josephson junction including only a domain-wall ferromagnet and a homogeneous ferromagnetic layer, which in addition to simplicity regarding the magnetization profile also offers a tunable long-range spin-triplet supercurrent. Finally, we discuss some experimental aspects of our findings.

cond-mat.supr-con↗

arXiv2009

Spin-polarized Josephson current in SFS junctions with inhomogeneous magnetization

SHORTENED ABSTRACT: We study numerically the properties of spin- and charge-transport in a nanoscale diffusive superconductor$\mid$ferromagnet$\mid$superconductor junction when the magnetization texture is non-uniform. Specifically, we incorporate the presence of a Bloch/Neel domain walls and conical ferromagnetism, including spin-active interfaces. The superconducting leads are assumed to be of s-wave type. 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. 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. 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 $I_c(ϕ) = -I_c(2π-ϕ)$, the spin-current satisfies $I_s(ϕ) = I_s(2π-ϕ)$, where $ϕ$ is the superconducting phase difference.

cond-mat.supr-con↗

arXiv2009

Phase-controlled proximity-effect in ferromagnetic Josephson junctions: calculation of DOS and electronic specific heat

We study the thermodynamic properties of a dirty ferromagnetic S$\mid$F$\mid$S Josephson junction with s-wave superconducting leads in the low-temperature regime. We employ a full numerical solution with a set of realistic parameters and boundary conditions, considering both a uniform and non-uniform exchange field in the form of a Bloch domain wall ferromagnetic layer. The influence of spin-active interfaces is incorporated via a microscopic approach. We mainly focus on how the electronic specific heat and density of states (DOS) of such a system is affected by the \textit{proximity effect}, which may be tuned via the superconducting phase difference. Our main result is that it is possible to \textit{strongly modify the electronic specific heat} of the system by changing the phase difference between the two superconducting leads from 0 up to nearly $π$ at low temperatures. An enhancement of the specific heat will occur for small values $h\simeqΔ$ of the exchange field, while for large values of $h$ the specific heat is suppressed by increasing the phase difference between the superconducting leads. These results are all explained in terms of the proximity-altered DOS in the ferromagnetic region, and we discuss possible methods for experimental detection of the predicted effect.

cond-mat.supr-con↗