Topological insulators: Star material

 A topological insulator sounds simple enough:  A block of material that lets electrons move along its surface, but not through its inside . In fact, it is far from straightforward. Ordinary metals conduct electrons all the way through, whereas ordinary insulators don't conduct electrons at all. A copper-plated block of wood conducts only on the surface, but that is two materials, not one. The idea of a topological insulator is so strange that for a long time, physicists had no reason to believe that such a material would exist .

 Researchers also believe that the collective motions of electrons inside topological insulators will mimic several of the never-before-seen particles predicted by high-energy physicists. Among them are axions, hypothetical particles predicted in the 1970s; magnetic monopoles, single points of north and south magnetism; and Majorana particles — massless, chargeless entities that can serve as their own antiparticles. 

First images of a carbon atom's electron clouds

The images were captured by  Igor Mikhailovskij 's team at the Kharkov Institute of Physics and Technology, Ukraine.

The uncalculability of electron systems

The electric and magnetic properties of solids are impossible to calculate exactly: The complex interactions of the many electrons which underly these phenomena cannot be computed even by the most powerful classical computers. Here, the central task is to determine the ground state of the electrons moving in the field of the positively charged nuclei. The most widely used method for treating such systems is Density Functional Theory, which reduces the many-body problem to a single particle interaction. As Dr. Norbert Schuch, scientist in the theory division of Prof. Ignacio Cirac at the Max Planck Institute of Quantum Optics in Garching, and Prof. Frank Verstraete from the University of Vienna, report in Nature Physics ( DOI: 10.1038/NPHYS1370 ), there exist however fundamental limitations to the applicability of this theory. The scientists succeeded by using methods developed in Quantum Information Theory, demonstrating that these methods can give deep insights beyond the development of quantum computers.

Escuela Franco-Venezolana de Nanotecnología 2009 ( ENANO2009 ) del 2 al 6 de noviembre de 2009 en Caracas y Choroní, Venezuela

Contacto

http://www.redvnano.org/congreso/contactanos.html

La Red Venezolana de Nanotecnología está ayudando a organizar la Escuela Franco-Venezolana de Nanotecnología 2009 ( ENANO2009 ) del 2 al 6 de noviembre de 2009 en Caracas y Choroní ( Venezuela ), bajo el patrocinio de:

• FONACIT
• Programa de Cooperación de Postgraduados ( PCP )
• Embajada de Francia en Caracas
• Fundación IDEA
• Academia de Ciencias Físicas, Matemáticas y Naturales
• Universidad Central de Venezuela

Para el primer día del evento ( 2/11/09 ) se ha programado una jornada en la Fundación IDEA ( Caracas, Venezuela ) en la cual varios investigadores presentarán los desarrollos obtenidos fruto de la cooperación franco-venezolana en nanociencia y nanotecnología, gracias al apoyo de las herramientas de cooperación científica entre estos dos países.

El Comité Organizador de la ENANO2009 también ha programado sesiones de cursos, charlas y carteles del 3 al 6 de noviembre de 2009. Esta segunda parte de la Escuela tendrá lugar en Choroní, Edo. Aragua. Las sesiones van dirigidas a estudiantes e investigadores sensibles al desarrollo de estos conocimientos en Venezuela.

Se programarán además mesas de trabajo sobre aspectos asociados al programa de doctorado interinstitucional de nanotecnología que la Red se encuentra promoviendo, la cooperación nacional e internacional en actividades de I+D+i dirigidas a atender los problemas de interés nacional, la definición de mecanismos que faciliten la comunicación entre el sector científico, productivo y la sociedad en general.

Formalismo de Keldysh (Keldysh Technique)

This technique provides the correct evaluation of the quantum mechanical average of an observable. It means that there is not any assumption about the final system state whenever we perform the above mentioned average. As a consequence, it is a suitable tool to study small systems in contact with macroscopic systems which are in "different" thermodynamic equilibrium states.

See the original Keldysh's papers:

• L. V. Keldysh, ZhEFT 47, 1515 (1964)
• L. V. Keldysh, Soviet Physics JEPT 20, 1018 (1965)

Electrons in graphene: an interacting fluid par excellence

Ever since it was shown that graphene—a single layer of carbon atoms—could be isolated from graphite, it has occupied a center stage of condensed matter physics. The popularity of graphene is rooted in the unusual nature of its low-energy excitations: near the Fermi level, the electron energies scale linearly with their momenta. This means that the electrons can be described as massless fermions, though with a velocity of about 300 times less than the velocity of light. The linear dispersion relation also implies a vanishing density of single-particle states at the Fermi level, which should make the effects of the Coulomb interaction between electrons weak.

Tunable few-electron double quantum dots and Klein tunnelling in ultraclean carbon nanotubes

Quantum dots defined in carbon nanotubes are a platform for both basic scientific studies and research into new device applications. In particular, they have unique properties that make them attractive for studying the coherent properties of single-electron spins. To perform such experiments it is necessary to confine a single electron in a quantum dot with highly tunable barriers, but disorder has prevented tunable nanotube-based quantum-dot devices from reaching the single-electron regime. Here, we use local gate voltages applied to an ultraclean suspended nanotube to confine a single electron in both a single quantum dot and, for the first time, in a tunable double quantum dot. This tunability is limited by a novel type of tunnelling that is analogous to the tunnelling in the Klein paradox of relativistic quantum mechanics.

Pauling’s dreams for graphene

Graphene research is probably one of the fastest growing fields in condensed matter physics.

1. The material is one atom thick, albeit it can be seen with an ordinary optical microscope.
2. It has the properties of a good metal, although its electronic properties do not fit the standard theory of metals because its electrons propagate as massless Dirac particles.
3. Graphene is also resistant against extrinsic impurities because its chemical bonding is very specific and consequently graphene conducts electricity better, with less energy loss, than silicon (the platform of all modern electronics).
4. Moreover, graphene is one of the strongest materials ever measured in terms of Young’s modulus and elastic stiffness (the only other material that is comparable in strength is diamond), nevertheless it is one of softest (the only example of a metallic membrane).
5. It can be used as an ultrasensitive nano-mechanical resonator besides being highly impermeable. Hence it is not surprising that so many high-tech industries are interested in developing graphene-based devices for a plethora of applications, from high-frequency transistors to reversible hydrogen storage.

Bottom-up Nanoconstruction by the Welding of Individual Metallic Nanoobjects Using Nanoscale Solder

We report that individual metallic nanowires and nanoobjects can be assembled and welded together into complex nanostructures and conductive circuits by a new nanoscale electrical welding technique using nanovolumes of metal solder.

At the weld sites, nanoscale volumes of a chosen metal are deposited using a sacrificial nanowire, which ensures that the nanoobjects to be bonded retain their structural integrity. We demonstrate by welding both similar and dissimilar materials that the use of nanoscale solder is clean, controllable, and reliable and ensures both mechanically strong and electrically conductive contacts. Nanoscale weld resistances of just 20Ω are achieved by using Sn solder. Precise engineering of nanowelds by this technique, including the chemical flexibility of the nanowire solder, and high spatial resolution of the nanowelding method, should result in research applications including fabrication of nanosensors and nanoelectronics constructed from a small number of nanoobjects, and repair of interconnects and failed nanoscale electronics.

A Molecular Linear Motor Consisting of Carbon Nanotubes

We experimentally investigated a “molecular-linear-motor” system consisting of a capsule-like carbon nanotube (CNT) in the interior space of a host CNT. Transmission electron microscopy revealed the capsule traveled back and forth between both ends of the hollow space along the axial direction and rotated simultaneously. The mechanism was well explained with molecular dynamics simulation by considering the driving force supplied from thermal energy. The present system operates around room temperature and this opens up the possibility of designing novel nanodevices such as oscillators and switching memory devices.

Quantum Dot Behavior in Graphene Nanoconstrictions

Graphene nanoribbons display an imperfectly understood transport gap. We measure transport through nanoribbon devices of several lengths. In long (≥250 nm) nanoribbons we observe transport through multiple quantum dots in series, while shorter (≤60 nm) constrictions display behavior characteristic of single and double quantum dots. New measurements indicate that dot size may scale with constriction width. We propose a model where transport occurs through quantum dots that are nucleated by background disorder potential in the presence of a confinement gap.