Notable results in nanoscience

Articles in other languages

Superconductivity in a single molecule transistor, français, 30 April 2010

Recent progress in the field of molecular electronics now allows for directly integrating molecular objects into electrical on-chip circuits. For example, by inserting molecules into a nanometer gap sectioning a metallic wire, it is possible to create a molecular bridge for electronic conduction. The surrounding electrostatic field (the gate) allows for tuning the position of the discrete molecular energy levels with respect to the Fermi energy of the contacts. Bringing these on and off resonance switches the molecular transistor on and off. By chemical engineering of the molecule’s size and optical, electronic or magnetic properties, one can obtain a vast variety of new functionalities.

Electronic transport through GaN quantum dots in nanowires, français, 30 April 2010

Nanowires are considered both as promising building blocks for nano-scale devices and as an alternative route to access the physics of low dimensional systems. In III-N materials, the strain relaxation offered by nanowires overcomes the typical problem of high dislocation density. Furthermore, III-N nanowire heterostructures have opened a new pathway to create III-N quantum dots with a flexibility to tune the dot height and to adjust the material composition without the requirement of lattice mismatch as the quantum dot grown by in Stranski Krastanow growth mode. Currently, most of the studies on III-N quantum dots are oriented towards photonic aspects, while there are very few works focusing on probing such structures via electrical means.

Heat flux at the nanoscale: beyond the Boltzmann-Stefan law, français, 20 May 2010

Does the usual Stephan-Boltzmann theory for blackbody radiation applies to nanometer-size objects ? To answer this question the heat flux in vacuum between two surfaces at different temperature and separated by distances between a micrometer to100 nm have been measured and compared to theory by two CNRS labs (Charles Fabry of Institut d’Optique and Institut Néel). At the nanometer scale, the measurements show large discrepancies with the Stefan-Boltzmann theory which describes this thermal exchange at large distances on the basis of Planck’s law. As well known, in the far field regime the heat flux exchanged between two flat parallel surfaces does not depend upon the distance between the two surfaces. Instead, in the near field regime, the measured variation is strong. The flux increase dramatically as the distance between the two surfaces becomes smaller than about one micrometer.

Measurement of quantum phase-slips in a Josephson junction chain, français, 21 May 2010

Josephson junction chains attract currently a lot of interest due to their possible applications in metrology or quantum information. For example, under microwave irradiation of frequency f, such chains could exhibit current quantization I=2nef where 2e is the charge of a Cooper pair and n is an integer number. They could be used for the definition of a new quantum current standard. In view of the potential applications, we have measured the ground state of a Josephson junction chain. Here we have analysed our results in terms of “quantum phase-slips”, the central phenomenon governing these superconducting networks.

Confirmation expérimentale des théories sur la surfusion ou pourquoi l’eau ne gèle pas dans les nuages, français, 21 May 2010

Des scientifiques de l’INAC, de l’Institut Néel et de l’ ESRF apportent des éléments clés pour expliquer le curieux phénomène de surfusion, cet état de la matière où un liquide ne gèle pas alors même qu’il est à une température inférieure à son point de cristallisation. La surfusion est un phénomène que l’on peut observer au quotidien puisque les nuages sont une accumulation de gouttelettes d’eau en surfusion.