A. Yu. Kasumov

Superconductivity in Ropes of Single-Walled Carbon Nanotubes

We report measurements on ropes of single-walled carbon nanotubes (SWNT) in low-resistance contact to nonsuperconducting (normal) metallic pads, at low voltage and at temperatures down to 70 mK. In one sample, we find a 2 orders of magnitude resistance drop below 0.55 K, which is destroyed by a magnetic field of the order of 1 T, or by a dc current greater than 2.5 microA. These features strongly suggest the existence of superconductivity in ropes of SWNT.

Thickness and low-temperature conductivity of DNA molecules

We argue that interaction between molecules and substrate is a key parameter which determines the conducting or insulating behavior of DNA molecules. In this letter, we show that strongly deformed DNA molecules deposited on a substrate, whose thickness is less than half the native thickness of the molecule, are insulating, whereas molecules keeping their native thickness are conducting down to very low temperature with a non-ohmic behavior characteristic of a 1D conductor with repulsive electron–electron interactions.

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.

Measurement of Quantum Noise in a Carbon Nanotube Quantum Dot in the Kondo Regime

The current emission noise of a carbon nanotube quantum dot in the Kondo regime is measured at frequencies ν of the order or higher than the frequency associated with the Kondo effect k(B)T (K)/h, with TK the Kondo temperature. The carbon nanotube is coupled via an on-chip resonant circuit to a quantum noise detector, a superconductor-insulator-superconductor junction. We find for hν ≈ k(B)T(K) a Kondo effect related singularity at a voltage bias eV ≈ hν, and a strong reduction of this singularity for hν ≈ 3k(B)T(K), in good agreement with theory. Our experiment constitutes a new original tool for the investigation of the nonequilibrium dynamics of many-body phenomena in nanoscale devices.

The effect of self-ions bombardment on the structure and properties of thin metal films

Metal films were deposited by the partially ionized beam technique, using a source with high ionization efficiency. Some characteristics of the source were investigated. Metals with low, medium and high melting temperatures were used for deposition. It was found that ionization efficiency of low-melting metals is higher than that of metals with medium and high-melting temperatures. The effect of the amount of self-ions in the beam of a deposited material as well as the effect of their energy on the structure and properties of the resulting films were studied.

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.

Alteration of superconductivity and radial breathing modes in suspended ropes of carbon nanotubes by organic polymer coatings

We have altered the superconductivity of a suspended rope of single walled carbon nanotubes, by coating it with organic polymers. Upon coating, the normal state resistance of the rope changes by less than 20 percent. But superconductivity, which on the bare rope shows up as a substantial resistance decrease below 300 mK, is gradualy suppressed. We correlate this to the suppression of radial breathing modes, measured with Raman Spectroscopy on suspended Single and Double-walled carbon nanotubes. This points to the breathing phonon modes as being responsible for superconductivity in carbon nanotubes.

Effect of Premelting on Conductivity of DNA-Lipid Films

We have measured temperature-dependent (between 20 and 80∘C) electrical conductivity and molecular structure (Raman spectroscopy) of DNA-lipid cast film. Our findings show that the conductivity is strongly influenced by premelting effects in the molecular structure starting near physiological temperatures (∼40∘C), prior to the global DNA denaturation.

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.