Suspended carbon nanotubes as electronical and nano-electro-mechanical hybrid systems in the quantum limit

Ultra clean and freely suspended carbon nanotubes provide an ideal model system for electronical transport measurements, and for the investigation of the interplay with their mechanical vibration in the quantum limit. Within the scope of this thesis both the excelling electronical and mechanical properties of carbon nanotubes clamped between metal contacts have been investigated. At cryogenic temperatures a quantum dot is formed on the suspended part of the nanotube, where ground and excited state spectroscopy could be performed. Here one has access even to the very first excess electron on the quantum dot, where the magnetic field dependence of the excited states directly provides the single particle energy spectrum, including curvature induced spin-orbit coupling and KK’ valley mixing. These coupling mechanisms lift the carbon nanotube specific fourfold degeneracy and induce a level splitting which gives rise to an unconventional Kondo effect in the intermediate coupling regime. Tracing these Kondo resonances in dependence on a parallel and perpendicular magnetic field reveal a hitherto unobserved many-body selection rule based on the discrete symmetries of the electronic carbon nanotube system. In addition, the transversal vibration mode of this doubly clamped nano-resonator is actuated and detected, and used to probe the dependence of the mechanical vibration on the quantum dot charging state and on an external magnetic field. Due to the high mechanical quality the electro-mechanic coupling in different transport regimes –ranging from the Fabry-Pérot via the intermediate coupling to the Coulomb blockade dominated few electron regime- could be analyzed in high precision. Finally first superconducting coplanar waveguide resonators have been fabricated and characterized, which form the harmonic component for future circuit-quantum-electro-dynamics experiments with carbon nanotube structures. The coupling of such microwave resonators to a carbon nanotube mechanical resonator, which possesses excelling properties as a high resonance frequency, a low mass density, and an exceptional high zero-point motion amplitude, enables ground state cooling and thus access to non-classical state preparation and manipulation in a mesoscopic system