A quantum dot is a tiny region of a semiconductor material, containing a small number of strongly interacting electrons. The dot can be connected to source and drain contacts (usually electrodes composed of NORMAL metals). The physics of transport through quantum dots reveals many interesting features which are at the front of contemporary condensed matter physics. It combines fundamental concepts in quantum mechanics and many body aspects. One of them is the Kondo effect[1], which is known to occur in metals containing a small amount of magnetic atoms.

  Recently, an experiment in which a quantum dot (in fact, a carbon nano-tube) is attached to SUPERCONDUCTING leads has been reported[2]. It demonstrates an intimate relation (in fact, a competition) between the Kondo effect and the presence of the superconducting gap. We will briefly review the theoretical framework for the underlying physics[3], and discuss also the situation where the electrodes are composed of "unconventional" superconductors[4].

[1] D. Goldhaber-Gordon et. al., Nature 391, 156-159 (1998). S. M. Cronenwett et al., Science 281, 540-544 (1998).
[2] M. R. Buitelaar et al. Phys. Rev. Lett. 89, 256801 (2002).
[3] Y. Avishai, A. Golub and A. D. Zaikin, Phys. Rev. B63 13-4515 (2001).
[4] T. Aono, A. Golub and Y. Avishai, Rev. B68 045312 (2003).