Title: First principles based theory of magnetic impurities embedded onto the surface of superconducting host, an application to MnNb(110)
Abstract: In this talk I describe a new, first-principles-based theory of magnetic impurities on superconducting surfaces and multilayers. I show how the Green's function embedding technique, commonplace in multiple scattering theory, can be extended to the fully relativistic Bogoliubov-de Gennes equation in such systems. The resulting theory is used to study the Yu-Shiba-Rusinov (YSR) states in the atomic monomer and dimers of Mn on top of Nb surfaces. The results are compared to recent experimental findings and previous tight-binding calculations. We also investigate the formation of the YSR states in the presence of different magnetic configurations and exchange magnetic fields and study the effect of spin-orbit coupling as well.
Recently it was suggested that certain perturbations of integrable spin chains lead to a weak breaking of integrability in the sense that integrability is preserved at the first order of the coupling. Here we examine this claim using level spacing distribution. We find that the volume dependent cross-over between integrable and chaotic statistics is markedly different between weak and strong breaking of integrability, supporting the claim that perturbations by generalised currents only break integrability at higher order. In addition, for the massless case we find that the critical coupling as a function of the volume L scales with a 1/L^2 law for weak breaking as opposed to the previously found 1/L^3 law for the strong case.
In this talk, I will discuss two different aspects of time-periodic (Floquet) systems. In the first, I will show how group theory can be applied to periodically-driven systems to impose selection rules on non-linear optical processes. In the second, I will discuss how a sudden quench into a superconducting state can give rise to large-scale Higgs oscillations, and how those, in turn, affect the optical properties of the material.