Spin effects in single-electron transport through carbon nanotube quantum dots

We investigate the total spin in an individual single-wall carbon nanotube quantum dot with various numbers of electrons in a shell by using the ratio of the saturation currents of the first steps of Coulomb staircases for positive and negative biases. The current ratio reflects the total-spin transition that is increased or decreased when the dot is connected to strongly asymmetric tunnel barriers. Our results indicate that total spin states with and without magnetic fields can be traced by this method.Comment: 5pages, 5figures, accepted for publication in Phys. Rev.

Superconducting SET with tunable electromagnetic environment

We have studied the environmental effect on superconducting single-electron transistors (S-SETs) by biasing S-SETs with arrays of small-capacitance dc SQUIDs, whose effective impedance can be varied in situ. As the zero-bias resistance of the arrays is increased, Coulomb blockade in the S-SET becomes sharper, and the gate-voltage dependence changes from e-periodic to 2e-periodic. The SQUID arrays could be used as on-chip noise filters.Comment: 2 pages, 3 embedded figures, submitted to LT23 proceedings. Error in Fig. 1 has been fixe