Senior Researcher, Center for Biomolecular Nanotechnologies, Italian Institute of Technology (IIT), Arnesano (Lecce), Italy.

Speech Title: Superconducting Sprintronics---Artificial spin triplet in a controllable superconductor/ferromagnet heterostructure
Abstract: Artificially juxtaposing antagonistic phenomenon such as superconductivity and ferromagnetism can lead to a variety of new quantum states. One possible state in the above example is the conversion of a conventional singlet s-wave Cooper pair into an s- wave triplet state. The electrons in a singlet Cooper pair scattering from a superconductor/ferromagnet interface are able to penetrate different distances depending on their spin direction relative to the ferromagnet. This creates a phase difference between the electrons, converting the singlet into a triplet. This triplet superconductivity, although spatially localised, is not based on strong correlations and as such can be studied under the framework of the BCS theory. In regions where both the triplet and singlet Cooper pairs are present a magne1tic moment is induced which is proportional to the product of their densities¹ .
Several recent experiments have used a superconductor in proximity to a non-collinear magnetic structure to create a spin aligned triplet state² . The non-collinear magnetic structure effectively takes the triplet described above and rotates the principle spin axis, projecting a triplet whose spins are aligned with respect to the new spin axis direction. Such a state no longer feels the paramagnetic pair breaking interaction of the exchange field of the ferromagnet, thus its coherence length is amplified by orders of magnitude.
We have designed heterostructure systems with triplet generation controllable with the application of a weak external magnetic field³ . In this work we present a study of the magnetic moment induced by the presence of the singlet and triplet states. We have used muon spin rotation spectroscopy (µSR) and polarised neutron reflectivity (PNR) to observe the modification of the magnetic state of the system below the transition temperature of the superconductor.
References
1. Bergeret, F. F., Volkov, A. & Efetov, K. K. Odd triplet superconductivity and related phenomena in superconductor-ferromagnet structures. Rev. Mod. Phys. 77, 1321– 1373 (2005).
2. Robinson, J. W. A., Witt, J. D. S. & Blamire, M. G. Controlled injection of spin-triplet supercurrents into a strong ferromagnet. Science 329, 59–61 (2010).
3. Flokstra, M. G., Kim J., et al. Remotely induced magnetism in a normal metal using a superconducting spin-valve" Nature Phys., 12, 57–61 (2016)