The work performed in the project has achieved most of its objectives and milestones both into the scientific and training objectives. In particular:
1-The material search was pursued to find the best candidates for solid-state diffusion tests including: InAs, Ge, NiBr2 as semiconductors and Al, Al/EuS as superconductors.
-It was found that InAs nanowires (NW), as opposed to Ge NWs, suffer from As degassing during the annealing process. That degrades the crystal quality of the nanowire itself because of the formation of voids which were observed in TEM imaging. A solutions was to anneal the samples in As over pressure. The results were presented at a specialistic conference.
-Investigations on Al/EuS thin demonstrated that the ferromagnetic insulator (EuS) able to induce magnetic correlations in the adjacent superconducting Al. Tests on thin films demonstrated superconductivity and strong magnetism in the Al. The non-reciprocal spintronic transport is at the base of two publications and the Patent.
-In the last part of the project, the van-der-Waals 2D semiconductor NiBr2 has been investigated. We observed non-reciprocal superconductivity it in the NiBr2/Al system and this scientific result is now in preparation for publication.
2. Ultra-short JJ: Fabrication and characterization of the first JJ with the solid-state diffusion technique.
The fabrication and electrical characterization of the devices was developed thanks to the interplay between the CNRS in Grenoble and the CNR-NEST in Pisa. Ther successful propagation of Al in to InAs is achieved from both ends, using rapid thermal annealing at 410°C for 15-35 min with subsequent observations in SEM and high angle annular dark field (HAADF) scanning TEM (STEM). Results of this technique have been presented at a Conference.
3. Demonstration of supercurrent-diodes and tunnel-diodes.
The characterization of Al/EuS films allowed the discovery of the non-reciprocal properties of spin-selective tunnel barriers. This result was disseminated through a publication and three conferences. Moreover, this result is at the base of a promising superconducting diode prototype that has been protected via a Patent. Finally, non-reciprocal superconductivity has been also observed in the supercurrent of Al/NiBr2 thin films measured at low temperature in the presence of strong in-plane magnetic fields stemming for magneto-chiral superconductivity, publication in progress.
4. Training in Superconductor physics. The researcher has been trained in the field of superconductor physics which is the main expertise of the hosting lab CNR Pisa. The focus was on the theoretical understanding of superconducting spintronics for applied electronics including non-reciprocal superconductivity and detectors. Intellectual property exploitation has also taken place and training of the researcher in the procedures for patenting.
5. Training in superconducting electronic transport characterization. The researcher has been introduced and fully trained in the experimental technique for quantum transport measurements at ultra-cryogenic temperature (<10mK) and at high magnetic fields (~Tesla). This included the mastering of cryogen-free dilution fridges equipped with single or vectorial magnets, for which she wrote user manuals and followed maintenance operations. She was also trained in the use of the low noise electronics for low and medium frequency (<100 kHz) characterizations.
