Thursday, December 21st - h. 15.00

Auditorium Bruno Touschek


A. Yu. Kasumov

(Starlab, Brussels)


Superconductivity in molecular wires




Superconductivity in molecular systems (inorganic and organic) has been studied for 25 years on macroscopic samples consisting of a huge amount of molecules. In this report we present the results of experimental study of superconductivity in individual molecules of carbon nanotubes and DNAs.

We show experimental evidence of induced and intrinsic superconductivity in carbon nanotubes. The supercurrent is observed in a single 1nm diameter SWNTs, in individual crystalline ropes containing about 100 nanotubes and also on multiwalled tubes.

These samples are suspended as strings between two superconducting (double layer Au-Re, Au-Ta or Sn film) and normal (double layer Au-Pt film) electrodes. The critical current of samples, extensively studied as function of temperature and magnetic field, presents unusual features which are not observed in ordinary Superconducting-Normal-Superconducting junctions and can be related to the strong 1D character of these samples.

We also show evidence of a huge sensitivity of dc transport properties of tubes to electromagnetic radiation in the radio-frequency range. We have performed conductivity measurements on double-stranded DNA molecules deposited by a combing process across a submicron slit between rhenium carbon metallic contacts. Conduction is ohmic between room temperature and 1 K. The resistance per molecule is less than 100 kohm and varies very slowly with temperature.

Below 1K, which is the superconducting transition temperature of the contacts, we observe proximity induced superconductivity. This implies in particular that DNA molecules can be metallic down to mK temperature, and furthermore that phase coherence is achieved over several hundred nanometers.



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MCD, 11/12/2000