prof. dr hab. Tadeusz Domański (UMCS, Lublin)

Andreev and Majorana-type quasiparticles in nanoscopic systems

It is well known that the electronic states of isotropic superconductors are prohibited inside some characteristic energy window Delta ~ meV around the Fermi surface because of electron pairing. Similar property has been recently observed in various nanoscopic objects (e.g. molecules, nanowires, carbon nanotubes, self-assembled quantum dots) due to the proximity effect, where the penetrating Cooper pairs convert them into superconducting nanoislands. The proximized nanoobjects often reveal formation of the additional in-gap (subgap) bound states. These Andreev-Yu-Shiba-Rusinov quasiparticles appear always in pairs because they represent coherent superpositions of the particle and hole states. Under specific conditions (due to spin-orbit coupling and external magnetic field) some of the in-gap states may evolve into the Majorana-type quasiparticles. In fact, the first experimental signature of the zero-energy Majorana feature has been reported by the Dutch group from Delft using InSb wire deposited on the s-wave NbTiN superconductor [V. Mourik et al, Science 336, 1003 (2012)]. I shall give a survey on the recent intensive studies of the Andreev/Majorana quasiparticles in nanoscopic systems. I will also discuss some closely related studies on the Cooper pair splitters, where the released/depaired electrons preserve their quantum entanglement over macroscopic scales.