Role of magnetic and nonmagnetic impurities in unconventional behavior of Ising superconductors

Apart from their signature giant anistotropy of the critical field, Ising superconductors (IS) exhibit other rather unexpected properties: (1) in tunneling through a ferromagnetic barrier, NbSe₂ IS demonstrates anticorrelaton between the tunneling gap value and gap broadening, internal hysteretic behavior that sets 2 K below T_c, spontaneous breaking of the C₆ symmetry (interpreted originally as"nematic superconductivity") and (2) NbSe₂ IS shows nonmonotonic behavior of Tc and Δ as a function of Se⇒S (initially interpreted as "multifractal superconductivity") and Nb⇒Mo doping . We show, utilizing results of first principle and model calculations, that all these effects are consequence of highly nontrivial interaction of IS with magnetic and nonmagnetic impurity. In this talk we will discuss (1), while (2) will be presented in the following talk by D. Wickramaratne. Finally, we will briefly discuss some nontrivial predictions/suggestions for new experiments that follow from the presented theory.