We present electronic transport measurements of a single wall carbon nanotube quantum dot coupled to Nb superconducting contacts. For temperatures comparable to the superconducting gap peculiar transport features are observed inside the Coulomb block
ade and superconducting energy gap regions. The observed temperature dependence can be explained in terms of sequential tunneling processes involving thermally excited quasiparticles. In particular, these new channels give rise to two unusual conductance peaks at zero bias in the vicinity of the charge degeneracy point and allow to determine the degeneracy of the ground states involved in transport. The measurements are in good agreement with model calculations.
Understanding the interplay between many-body phenomena and non-equilibrium in systems with entangled spin and orbital degrees of freedom is a central objective in nano-electronics. We demonstrate that the combination of Coulomb interaction, spin-orb
it coupling and valley mixing results in a particular selection of the inelastic virtual processes contributing to the Kondo resonance in carbon nanotubes at low temperatures. This effect is dictated by conjugation properties of the underlying carbon nanotube spectrum at zero and finite magnetic field. Our measurements on a clean carbon nanotube are complemented by calculations based on a new approach to the non-equilibrium Kondo problem which well reproduces the rich experimental observations in Kondo transport.
Tunneling spectroscopy of a Nb coupled carbon nanotube quantum dot reveals the formation of pairs of Andreev bound states (ABS) within the superconducting gap. A weak replica of the lower ABS is found, which is generated by quasi-particle tunnelling
from the ABS to the Al tunnel probe. An inversion of the ABS-dispersion is observed at elevated temperatures, which signals the thermal occupation of the upper ABS. Our experimental findings are well supported by model calculations based on the superconducting Anderson model.
We investigate submicron ferromagnetic PdNi thin-film strips intended as contact electrodes for carbon nanotube-based spintronic devices. The magnetic anisotropy and micromagnetic structure are measured as function of temperature and aspect ratio. Co
ntrary to the expectation from shape anisotropy, magnetic hysteresis measurements of Pd0.3Ni0.7 on arrays containing strips of various width point towards a magnetically easy axis in the sample plane, but transversal to the strip direction. Anisotropic magnetoresistance measured on individual Pd0.3Ni0.7 contact strips and magnetic force microscopy images substantiate that conclusion.
We investigate quantum dots in clean single-wall carbon nanotubes with ferromagnetic PdNi-leads in the Kondo regime. In most odd Coulomb valleys the Kondo resonance exhibits a pronounced splitting, which depends on the tunnel coupling to the leads an
d an external magnetic field $B$, and only weakly on gate voltage. Using numerical renormalization group calculations, we demonstrate that all salient features of the data can be understood using a simple model for the magnetic properties of the leads. The magnetoconductance at zero bias and low temperature depends in a universal way on $g mu_B (B-B_c) / k_B T_K$, where $T_K$ is the Kondo temperature and $B_c$ the external field compensating the splitting.
We present an investigation of different thin-film evaporated ferromagnetic materials for their suitability as electrodes in individual single-wall and multi-wall carbon nanotube-based spin devices. Various electrode shapes made from permalloy (Ni_{8
1}Fe_{19}), the diluted ferromagnet PdFe, and PdFe/Fe bilayers are studied for both their micromagnetic properties and their contact formation to carbon nanotubes. Suitable devices are tested in low-temperature electron transport measurements, displaying the typical tunneling magnetoresistance of carbon nanotube pseudo spin valves.
