Manipulating the magnetic state of a carbon nanotube Josephson junction using the superconducting phase

par Richard DEBLOCK, Laboratoire de Physique des Solides, Université Paris-Sud

Le MARDI 13 Janvier à 14h, salle des séminaires, bâtiment A4, 3e étage

When a metal contains magnetic impurities, their associated moments can be screened by the conduction electrons, resulting in a singlet state. This many-body phenomenon is at the heart of the Kondo effect. If the metal is replaced by a superconductor, the singlet can be destroyed in favor of a magnetic doublet. This is accompanied by a sign change of the supercurrent in a junction geometry. This singlet-doublet transition was shown to depend on the relevant energy scales: the Kondo temperature and the superconducting gap, as well as the position of the impurity level. In the present work we show that the superconducting phase difference across a quantum dot can also control this magnetic transition of a Kondo impurity. We measured the relation between the supercurrent and the superconducting phase difference of a carbon nanotube Josephson junction. It exhibits distinctively anharmonic behavior, revealing the phase mediated singlet to doublet transition, in excellent agreement with finite temperature quantum Monte Carlo calculations and provides insights on the phase controlled level-crossing transition at zero temperature.