Direct Experimental Evidence of the Statistical Nature of the Electron Gas in Superconducting Films

In an Nb film an alternate electrical current is partitioned at a Y-shaped obstacle into two splitted beams. The intensity-fluctuation correlation of the two beams (cross-correlation) and the intensity- fluctuation correlation of one beam (auto-correlation) are measured within a low-frequency bandwidth as a function of the incident beam intensity, at temperatures T above or below the temperature Tc of the superconductive transition. The results of these measurements reveal the statistical nature of the electron gas in the normal film and in the superconducting film. The conceptual scheme of the present experiment is a version of the Hanbury Brown and Twiss (HBT) experiment, here adopted for a gas of particles in a solid

Anodization-based process for the fabrication of all niobium nitride Josephson junction structures

We studied the growth and oxidation of niobium nitride (NbN) films that we used to fabricate superconductive tunnel junctions. The thin films were deposited by dc reactive magnetron sputtering using a mixture of argon and nitrogen. The process parameters were optimized by monitoring the plasma with an optical spectroscopy technique. This technique allowed us to obtain NbN as well as good quality AlN films and both were used to obtain NbN/AlN/NbN trilayers. Lift-off lithography and selective anodization of the NbN films were used, respectively, to define the main trilayer geometry and/or to separate electrically, different areas of the trilayers. The anodized films were characterized by using Auger spectroscopy to analyze compounds formed on the surface and by means of a nano-indenter in order to investigate its mechanical and adhesion properties. The transport properties of NbN/AlN/NbN Josephson junctions obtained as a result of the above described fabrication process were measured in liquid helium at 4.2 K

Tranport properties of SW and MW carbon nanotube bundles

Abstract- Transport properties of single and multiwalled carbon nanotubes, with the tube axes aligned along the bias current direction, have been studied as a function of the temperature and applied current. The experimental data are consistent with a model of charge transport governed by tunnel between potential barriers created at the connection between the nanotubes or bundles surfaces and modulated by thermal fluctuations. A current dependence of the potential energy for both single and multiwalled samples that gives indications the charge transport mechanism inside these materials has been obtained. Moreover, the values of the potential energy found, less for multiwalled with respect to the single walled nanotubes, confirm the presence of a metallic component in the samples as shown from the temperature dependence resistivity data

Low Temperature Conductivity of Carbon Nanotube Aggregates

nanotubes arranged in the form of aligned arrays or in the form of fibres. The experimental data show that both the forms of aggregates present a crossover in the transport mechanism from three-dimensional hopping of the electrons between localized states at high temperature to fluctuation-induced tunnelling across potential barriers at low temperature. The role of the junctions formed between the bundles in the array and between the nanotubes inside the fibres is discussed on the basis of the experimental results