Josephson Effect through an isotropic magnetic molecule

Minchul Lee (1, 2) , Thibaut Jonckheere (1, 2) , Thierry Martin (1, 2)

1 CPT - Centre de Physique Théorique - UMR 6207
2 CPT - Centre de Physique Théorique - UMR 7332

We investigate the Josephson effect through a molecular quantum dot magnet connected to superconducting leads. The molecule contains a magnetic atom, whose spin is assumed to be isotropic. It is coupled to the electron spin on the dot via exchange coupling. Using the numerical renormalization group method we calculate the Andreev levels and the supercurrent and examine intertwined effect of the exchange coupling, Kondo correlation, and superconductivity on the current. Exchange coupling typically suppresses the Kondo correlation so that the system undergoes a phase transition from 0 to $\pi$ state as the modulus of exchange coupling increases. Antiferromagnetic coupling is found to drive exotic transitions: the reentrance to the $\pi$ state for a small superconducting gap and the restoration of 0 state for large antiferromagnetic exchange coupling. We suggest that the asymmetric dependence of supercurrent on the exchange coupling could be used as to detect its sign in experiments.

Mots clés: molecular electronics; spintronics; quantum dots; Kondo effect; numerical renormalization group; metallofullerene; Josephson effect

Domaines: Systèmes mésoscopiques et effet Hall quantique [cond-mat.mes-hall]

Minchul Lee, Thibaut Jonckheere, Thierry Martin. Josephson Effect through an isotropic magnetic molecule. Physical Review Letters, 2008, 101, pp.146804. ⟨hal-00276921v3⟩