Controllable pi junction in a Josephson quantum-dot device with molecular spin.

Colin Benjamin (1, 2) , Thibaut Jonckheere (1, 2) , Alex Zazunov (1, 3, 2) , Thierry Martin (1, 2)

1 CPT - Centre de Physique Théorique - UMR 6207
2 CPT - Centre de Physique Théorique - UMR 7332
3 LEPES - Laboratoire d'Etudes des Propriétés Electroniques des Solides

We consider a model for a single molecule with a large frozen spin sandwiched in between two BCS superconductors at equilibrium, and show that this system has a $\pi$ junction behavior at low temperature. The $\pi$ shift can be reversed by varying the other parameters of the system, e.g., temperature or the position of the quantum dot level, implying a controllable $\pi$ junction with novel application as a Josephson current switch. In contrast to previous works the importance of the contribution from the continuum of states above the superconducting gap is brought out. The free energy for certain configuration of parameters shows a bistable nature, which is a necessary pre-condition for achievement of a qubit.

Mots clés: molecular; spintronics; Josephson; supraconductivity; quantum dot; pi junction

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

Colin Benjamin, Thibaut Jonckheere, Alex Zazunov, Thierry Martin. Controllable pi junction in a Josephson quantum-dot device with molecular spin.. 2006. ⟨hal-00068625v3⟩