Our group focuses on the investigation of the physical properties of systems combinining superconductor (S) and ferromagnet (F) materials. Our research fits into the emerging research field currently known as ''superconducting spintronics'' which aims at developing electronic devices with high energy efficiency for large data centres and quantum technology applications.
The combination of S and F materials to realise superconducting spintronic devices is not trivial. This is because in a conventional S electrons pair up in a parallel-aligned spin (spin-singlet) state. Spin-singlet Cooper pairs, however, are short-ranged inside a F due to its exchange field which induces different phase shifts for the two spin orientations and therefore rapidly breaks the phase coherence necessary for a Cooper pair to survive.
The incompatibility between F and S materials can be overcome, however, by properly engineering S/F systems to have a magnetically-inhomogeneous F layer. In this case, through a combination of spin-mixing and spin-rotation processes, spin-singlet pairs can be converted into parallel-aligned spin (spin-triplet) pairs which are fully spin-polarised and long-ranged inside a F layer meaning that they can be used for superconducting spintronic applications.
After carrying out some of the earliest work demonstrating direct (spectroscopic) evidence for spin-triplet states in metallic S/F systems, Dr Di Bernardo has recently focused on engineering novel S/F systems and devices based on oxides and 2D materials. The integration of oxides and 2D materials in superconducting spintronics represents a fundamental step towards the development of devices with an extended range of functionalities and control modalities compared to exisisting ones, which are mainly based on metals.
A representative list of research projects which are currently carried out in Dr Di Bernardo's group is reported below. For further information about the projects listed and other projects available, please feel free to contact Dr Di Bernardo via email.
S/F heterostructures down to the 2D limit
The recent advent of 2D van-der-Waals (vdW) heterostructures combined with the possibility of exfoliating vdW materials down to the 2D limit paves the way for the investigation of superconducting systems in the two-dimensional (2D) regime. Based on our previous experience and results on materials systems and devices for the generation of spin-triplet states in three-dimensional (3D) thin film superconductor/ferromagnet (S/F) heterostructures, we are currently investigating S/F systems based on 2D materials.
The spectroscopic properties of 2DS/2DF systems are characterised using a combination of low-temperature scanning tunneling microscopy and tunnel junctions with a 2D transition metal dichalcogeneide barrier. In addition, we are charactericing the magnetotransport properties of 2DS/2DF combinations, with the aim of fabricating superconducting spintronics devices with novel properties and functionalities compared to their 3D equivalent. These projects are carried out in collaboration with Dr Steinberg from the Racah Institute of Physics, Prof. Ferrari from the Universtiy of Cambridge, and Prof. Scheer and Prof. Belzig from the University of Konstanz.
Unconventional superconductivity and magnetism probed by low-energy muon spectroscopy (LE-μSR)
The interplay between superconductivity and ferromagnetism can give rise to unusual tantalising physical phenomena. Using the high sensitivity of spin-polarised muon particles to magnetic fields (< 0.1 Gauss), we can detect unconvetional states originating from superconductivity and its interplay with magnetism, and study their depth dependence in multilayer thin film samples by varying the muon implantation energy in LE-μSR. Some of the ongoing projects concern study of magnetic states in metal-oxide materials (or combinations thereof) or in elemental superconductors with molecules. The beam time for each of these projects is awarded as result of a competitive application process at Paul Scherrer Institute (PSI) for beam time allocation, and it is done in collaboration with Dr Zaher Salman (main collaborator and support beamscientist at PSI), in addition to many other scientific partners from all around the world.