Screening clouds in Superconductors

Magnetic impurities coupled to conduction band can generate a many-body correlated screening cloud known as the Kondo cloud. In the presence of superconducting correlations, there can exist Yu-Shiba-Rusinov (YSR) phase in addition to the Kondo phase that can also generate screening clouds across the superconductor. Since, a conduction band can only screen one-half spin per channel, a large spin impurity coupled to the conduction band can generate what is known as the Underscreened Kondo effect. The spatial extension of the screening cloud in such a partially screened impurity coupled to a superconductor remains to be described.

Therefore, in this work, we focus on a large spin impurity coupled to a superconducting reservoir. We observe a doublet to triplet phase transition corresponding to the underscreened Kondo and YSR states in the system. Interestingly, the underscreened Kondo screening cloud shows additional properties resulting from the unscreened part of the impurity interacting with the superconductor. The screening imparted by the clouds and its spatial extension have been extracted using the Numerical Renormalization Group (NRG) method and the Density Matrix Renormalization Group (DMRG) method respectively.