arXiv subjects

S. Tollis

Publications and source records attributed to S. Tollis.

4 recordsLinked to original sources

arXiv2007

Josephson current in a superconductor -- ferromagnet -- superconductor junction with in-plane ferromagnetic domains

We study a diffusive superconductor--ferromagnet--superconductor (SFS) junction with in-plane ferromagnetic domains. Close to the superconducting transition temperature, we describe the proximity effect in the junction with the linearized Usadel equations. We find that properties of such a junction depend on the size of the domains relative to the magnetic coherence length. In the case of large domains, the junction exhibits transitions to the $π$ state, similarly to a single-domain SFS junction. In the case of small domains, the magnetization effectively averages out, and the junction is always in the zero state, similarly to a superconductor--normal metal--superconductor (SNS) junction. In both those regimes, the influence of domain walls may be approximately described as an effective spin-flip scattering. We also study the inhomogeneous distribution of the local current density in the junction. Close to the 0--$π$ transitions, the directions of the critical current may be opposite in the vicinity of the domain wall and in the middle of the domains.

cond-mat.mes-hall↗

arXiv2007

Josephson current in a superconductor-ferromagnet junction with two non-collinear magnetic domains

We study the Josephson effect in a superconductor--ferromagnet--superconductor (SFS) junction with ferromagnetic domains of non-collinear magnetization. As a model for our study we consider a diffusive junction with two ferromagnetic domains along the junction. The superconductor is assumed to be close to the critical temperature $T_c$, and the linearized Usadel equations predict a sinusoidal current-phase relation. We find analytically the critical current as a function of domain lengths and of the angle between the orientations of their magnetizations. As a function of those parameters, the junction may undergo transitions between 0 and $π$ phases. We find that the presence of domains reduces the range of junction lengths at which the $π$ phase is observed. For the junction with two domains of the same length, the $π$ phase totally disappears as soon as the misorientation angle exceeds $π/2$. We further comment on possible implication of our results for experimentally observable 0--$π$ transitions in SFS junctions.

cond-mat.supr-con↗

arXiv2005

Competition between Pi-coupling and FFLO modulation in SF/SF atomic thickness bilayers

We present the detailed theoretical study of a heterostructure comprising of two coupled ferromagnetic superconducting layers. Our model may be also applicable to the layered superconductors with alternating interlayer coupling in a parallel magnetic field. It is demonstrated that such systems exhibit a competition between the nonuniform Larkin-Ovchinnikov-Fulde-Ferrel (FFLO) state and the superconducting state where the sign of the superconducting order parameter is opposite in adjacent layers. We determine the complete temperature-field phase diagram both in the cases of low and strong interlayer coupling. In the former we obtain a new Pi-phase inserted within the FFLO phase and located close to the usual tricritical point, whereas in the latter the bilayer in the state reveals a very high paramagnetic limit and the phenomenon of field-induced superconductivity.

cond-mat.supr-con↗

arXiv2005

Field induced superconductivity with enhanced and tunable paramagnetic limit

We demonstrate that in a superconducting multilayered system with alternating interlayer coupling a new type of nonuniform superconducting state can be realized under in-plane magnetic field. The Zeeman effect in this state is compensated by the energy splitting between bonding and antibonding levels. Such compensation mechanism at low temperature leads to the field-induced superconductivity. We discuss the conditions for the experimental observation of the predicted phenomena.

cond-mat.supr-con↗