Seminarium Fizyki Materii Skondensowanej

Whenever quantum impurities are present in the bulk superconductors theyusually have a detrimental influence, either breaking the electron pairsor spoiling their long-range coherence. Recently a different kind ofrelationship attracts, however, a considerable amount of interest. Thereare numerous activities addressing the following question 'how can thesuperconducting reservoirs affect the quantum impurities if they arebrought in a contact ?'. In such circumstances the proximity effectspreads electron pairing onto the quantum impurities, converting them into'superconducting grains'. This effect plays a crucial role inhetero-structures, where the quantum dots are embedded between two (ormore) external reservoirs, forming the single electron transistors. Byvarying the gate potential one can then observe the quantum phasetransitions from the BCS-type to the singly occupied configurations.Furthermore, at sufficiently low temperatures also the Kondo physics canbe confronted with the electron pairing in a fully controllable manner [R.Maurand, Ch. Schonenberger, Physics 6, 75 (20013)]. I shall give a surveyon these and similar issues, both with regard tothe recent theoretical studies and experimental realizations.