Yu. A. Kasumov

Proximity effect in a superconductor-metallofullerene-superconductor molecular junction

We report low-temperature transport measurements through molecules of Gd metallofullerenes between superconducting suspended electrodes. The presence and number of molecules in the 2-nm-wide gap between electrodes was determined by high resolution transmission electron microscopy. We find that a junction containing a single metallofullerene dimer between superconducting electrodes displays signs of proximityinduced superconductivity. In contrast, no proximity effect develops in junctions containing a larger cluster of metallofullerenes. These results can be understood by taking into account multiple Andreev reflections, and the spin states of the Gd atoms.

Scanning and transmission electron microscope images of a suspended single-walled carbon nanotube

For the first time we perform simultaneous observations of individual single-walled carbon nanotubes using scanning electron microscope (SEM) and transmission electron microscope modes of a transmission electron microscope equipped with a scanning attachment operating at 100kV. We show that in the SEM mode both individual single-walled carbon nanotubes situated on thin Si3N4 membranes and portions of these tubes projecting far beyond the membranes can be observed. The contrast and width of the nanotube images depend on their diameter and density on a substrate. Possible mechanisms of the observed nanotube contrast are discussed.

Ballistic edge states in Bismuth nanowires revealed by SQUID interferometry

The protection against backscattering provided by topology is a striking property. In two-dimensional insulators, a consequence of this topological protection is the ballistic nature of the one-dimensional helical edge states. One demonstration of ballisticity is the quantized Hall conductance. Here we provide another demonstration of ballistic transport, in the way the edge states carry a supercurrent. The system we have investigated is a micrometre-long monocrystalline bismuth nanowire with topological surfaces, that we connect to two superconducting electrodes. We have measured the relation between the Josephson current flowing through the nanowire and the superconducting phase difference at its ends, the current–phase relation. The sharp sawtooth-shaped phase-modulated current–phase relation we find demonstrates that transport occurs selectively along two ballistic edges of the nanowire. In addition, we show that a magnetic field induces 0–π transitions and φ0-junction behaviour, providing a way to manipulate the phase of the supercurrent-carrying edge states and generate spin supercurrents.

Selective growth of single-wall carbon nanotubes and the fabrication of devices on their basis

Single-wall carbon nanotubes were synthesized on specified parts of oxidized silicon substrates by single acetylene burst CVD and studied with high-resolution scanning electron and scanning probe micro-scopes. The resistance of individual nanotubes and nanotube series was measured using devices fabricated by the deposition of Pd and Pd/Al electrodes on the obtained single-wall nanotubes. The contact potential difference between Pd electrodes and carbon nanotubes was measured in the Kelvin mode of a scanning probe microscope.

The effect of catalyst nanoparticle preparation techniques on the structure of carbon nanotubes

The effect of the composition, deposition method, and preliminary annealing temperature of catalyst thin films on the structure of catalyst nanoparticles and carbon nanotubes synthesized by CVD with a single acetylene burst was studied. A catalyst preparation technique was found that yields the narrowest distribution of the diameters of nanoparticles and of single-wall carbon nanotubes grown on them.

Proximity induced and intrinsic superconductivity in long and short molecules

Publisher Summary This chapter explains the proximity-induced superconductivity that has emerged as one of the most efficient tools of the investigation of phase coherent transport at mesoscopic or nanoscopic scales. Observing proximity effect in long molecular wires implies indeed not only that these molecules are conducting and form a low-resistance contact with superconducting electrodes, but also, which is more fundamental, that both the thermal length and the phase coherence length are of the order of the length of the molecules. The observation of the proximity effect yields the order of the magnitude of typical time- and length-scales involved in the charge transfer mechanism along the molecules. Conductivity measurements on double-stranded DNA molecules deposited by a combing process across a submicron slit between rhenium carbon metallic contacts have been conducted. In the case of carbon nanotubes on superconducting contacts, the observation of high supercurrents strongly suggests the existence of intrinsic superconducting fluctuations. This is corroborated by experiments on long ropes of carbon nanotubes on normal contacts.

Superconductivity in Long and Short Molecules

We present the results of experimental study of superconductivity in individual molecules of carbon nanotubes, DNAs and metallofullerenes. Critical currents of supeconductor‐molecule‐superconductor junctions were extensively studied as a function of temperature and magnetic field. The mechanism of current induced superconductor‐normal state transition for a long molecule (carbon nanotubes and DNAs) is the creation of phase slip centres and for a short molecule (metallofullerens) — multiple Andreev reflections. We observe an influence of spin state of encapsulated atom on the induced superconductvity in a metallofullerene molecule.