STAGE OFFRE DE STAGE : SUPERCURRENT AND DYNAMICS IN CARBON NANOTUBES

The aim of this internship is to measure the dynamics of nanoscale devices by coupling them on chip to a quantum detector. This quantum detection scheme is based on a superconducting tunnel junction. We will focus on the behavior of a carbon nanotube quantum dot connected to superconducting contacts.

A mesoscopic conductor connected to superconducting electrodes can sustain a supercurrent, which is a periodic function of the phase difference between the two superconductors. The amplitude and the phase-dependence of the supercurrent provide information on the nature and symmetry of the quantum states confined in the nanostructure. In the case of a quantum dot it becomes possible to probe an intriguing situation, in which the superconducting proximity effect competes with another type of electronic correlation: the Kondo effect. By finely tuning the coupling between the quantum dot and the electrodes, the spin of the dot’s highest occupied energy levels is screened by the electrodes’ conduction electrons. This constitutes a correlated singlet state between the dot’s spin and the electrodes. Such a correlated state forms below a characteristic temperature, the Kondo temperature TK, and leads to a resonance in the conduction properties of the quantum dot. For a quantum dot connected to superconducting contacts, this Kondo effects persists even when the superconducting gap ¿ is smaller than kBTK. In that case the two effects cooperate the supercurrent is largest (“junction 0”). I