We report the observation of two fundamental sub-gap transport processes through a quantum dot (QD) with a superconducting contact. The device consists of a carbon nanotube contacted by a Nb superconducting and a normal metal contact. First, we find
a single resonance with position, shape and amplitude consistent with the theoretically predicted resonant Andreev tunneling (AT) through a single QD level. Second, we observe a series of discrete replicas of resonant AT at a separation of $sim145,mu$eV, with a gate, bias and temperature dependence characteristic for boson-assisted, inelastic AT, in which energy is exchanged between a bosonic bath and the electrons. The magnetic field dependence of the replicas amplitudes and energies suggest that two different bosons couple to the tunnel process.
We present a fabrication scheme called fork stamping optimized for the dry transfer of individual pristine carbon nanotubes (CNTs) onto ferromagnetic contact electrodes fabricated by standard lithography. We demonstrate the detailed recipes for a res
idue-free device fabrication and in-situ current annealing on suspended CNT spin-valve devices with ferromagnetic Permalloy (Py) contacts and report preliminary transport characterization and magnetoresistance experiments at cryogenic temperatures. This scheme can directly be used to implement more complex device structures, including multiple gates or superconducting contacts.
Nanostructured superconductor/ferromagnet heterocontacts are studied in the different transport regimes of point-contact spectroscopy. Direct measurements of the nanocontact size by scanning electron microscopy allow a comparison with theoretical mod
els for contact-size estimates of heterocontacts. Our experimental data give evidence that size estimates yield reasonable values for the point-contact diameter $d$ as long as the samples are carefully characterized with respect to the local electronic parameters.
