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Posted: February 12, 2008
One electron makes all the difference
(Nanowerk News) A research team from the department of condensed matter physics of the Universidad Autónoma de Madrid working in collaboration with the research group lead by professor Christian Schoenenberger at the University of Basel in Switzerland, have discovered that just an electron sets the conductive properties of a carbon nanotube.
Since their discovery in 1991, carbon nanotubes have continually fascinated physicists and chemists with their amazing electronic and mechanical properties.
These cylindrical molecules with a radius of a few Angstroms and with lengths of up to several micrometers have endless applications inside different scientific fields from nanoelectronics to material science, and are used by scientists to study a wide range of physical phenomena that only take place at a nanometric scale. The combination of nanotubes and other materials form hybrid structures and these are of particular interest. For example, carbon nanotubes connected to superconductive electrodes (materials that offer no electrical resistance at low temperatures) are currently being used to study exotic physical phenomena like the Josephson Effect. This Nobel Prize winning discovery made by physicist Brian D. Josephson in 1973 consists of the almost magic effect of producing an electrical current in a superconductive junction without the application of a voltage.
In the last two three years several research groups have demonstrated that in a carbon nanotube held in between superconducting electrodes, the Josephson effect can be controlled at will, making possible a superconductive version of a transistor. This discovery has endless possibilities, most of which have barely started to be investigated.
A research group from the UAM working in collaboration with a research team lead by Christian Schoenenberger of Basilea University, has recently published an article in the Physical Review Letters, where a new phenomenon that takes place within these nanotube-superconductor structures has been described (" Even-Odd Effect in Andreev Transport through a Carbon Nanotube Quantum Dot").
Demonstrating that carbon nanotubes truly are an endless supply of new physical phenomena, they have discovered that when a voltage is applied to these hybrid structures, the electric current that flows depends greatly on the number of electrons that are present at the nanotube, and furthermore, whether this number is even or odd has a drastic impact. This new transport phenomenon is caused by subtle interactions between the Spins (magnetic field produced by the electrons as they rotate) of the electrons in the carbon nanotubes - a characteristic which depends on their number and the conducting electrons in the superconductor.