First-principles theory of superconducting heterostructures

Rövid cím: 
Theory of superconducting heterostructures
2016. 03. 18. 10:15
BME Elméleti Fizika Tanszék, F-épület, III lépcsőház, szemináriumi szoba
Balázs Újfalussy (Wigner Res. Inst.)

We show how Multiple Scattering Theory can be generalized to solve the Kohn-Sham-Bogoliubov-de Gennes equations for surfaces of supeconductors and their interfaces with normal metals. The theory is than applied to various overlayers where we show that in the energy range of the superconducting gap, the quasiparticle spectrum consists of Andreev bound states with a dispersion which is closely connected to the underlying electronic structure of the overlayer. We also find that the spectrum has a strongly k-dependent induced gap. In the case of thick superconducting layers we calculate the critical temperature based on the thickness dependence of the gap size and we compare it with with experiments on Au/Nb(100). In the case of thin superconductor layers, where the electron-phonon interaction may change significantly, we also calculate the layer dependent phonon spectrum to determine the layer dependence of the electron-phonon coupling. The theory is applied to niobium slabs and thin niobium-gold multilayers, where we investigate both the critical temperature and the inverse proximity effect observed in thin superconducting heterostructures.