In the first part of this thesis, we present a new approach to the fabrication of devices based on carbon nanotubes (CNTs) in the low disorder regime. Our fabrication method consists of growing CNTs on a transparent quartz chip and stamping them on an array of tens of devices. The quartz chip and the recipient chip are designed in such a way that during the stamping process the CNTs do not touch any substrate and stays suspended on the electrodes of the recipient devices. The parallel transfer of tens of CNTs highly increases the average number of usable devices per chip. The resulting CNT-based devices are characterized via transport measurements at different temperatures down to the milli-Kelvin regime. The separation of growth chip from the measurement chip allows one to freely choose the material for the electrodes, opening the way for the implementation of CNT-based devices with superconducting or ferromagnetic leads.
It was suggested recently that Majorana Fermions should emerge in CNTs contacted with a thin superconductor which retains its superconducting gap in presence of large in-plane field. We demonstrate an all-dry technique for contacting CNTs with few-layer-thick flakes of niobium diselenide (NbSe2) as superconducting layered material of the family of the transition metal dichalcogenides. The choice of NbSe2 is motivated by its large critical in-plane magnetic field. We show that the NbSe2-to-CNT contact resistance is comparable to that observed for other methods. We discuss the temperature and magnetic field dependence of the quantum transport in our devices. Furthermore, we could observe long-range superconducting correlations in a few micrometer-long CNT which is encapsulated in stack of NbSe2 and hexagonal boron nitride. We show that a substantial supercurrent flows through the nanotube section underneath the NbSe2 crystal and through a two-micrometer long portion which is not in contact with it. As predicted for superconductors with a cross section in the nanometer range, the current-triggered collapse of superconductivity is mediated by resistance steps due phase slip center nucleation.
The Ising superconductor NbSe2 is the ideal playground to examine the emergence of phase slip events. The exact nucleation position of phase slip lines in plain NbSe2 films is hard to predict and crucially depends on the individual sample. By patterning a one-dimensional constriction in NbSe2, the free energy barrier, which must be overcome to create a normal conducting region inside the superconducting 1D channel, will be sufficiently small. We demonstrate that as such fabricated nanowires still show superconducting features and that we can relate their origins to phase slip centers and lines
