Phase diagram and excitations of a Shiba molecule
  We analyze the phase diagram associated with a pair of magnetic impurities trapped in a superconducting host. The natural interplay between Kondo screening, superconductivity and exchange interactions leads to a rich array of competing phases, whose transitions are characterized by discontinuous changes of the total spin. Our analysis is based on a combination of numerical renormalization group techniques as well as semi-classical analytics. In addition to the expected screened and unscreened phases, we observe a new molecular doublet phase where the impurity spins are only partially screened by a single extended quasiparticle. Direct signatures of the various Shiba molecule states can be observed via RF spectroscopy. 
N. Y. Yao, C. P. Moca, I. Weymann, J. D. Sau, M. D. Lukin, E. A.   Demler, G. Zar\'and
cond-mat.supr-con cond-mat.mes-hall cond-mat.str-el