The quest for dilute ferromagnetism in semiconductors: Guides and misguides by theory

A material that exhibits both ferromagnetic and semiconductor properties offers the exciting prospect of combining nonvolatile magnetic storage and conventional semiconductor electronics in a single device. Magnetic semiconductors offer a number of interesting possibilities in the pursuit of  spintronics , a branch of science and technology that exploits the spin dimension of the electron in addition to its charge, for novel electronic devices. These materials combine the properties of a semiconductor and a magnetic material, providing, for instance, a way to create 100 % spin-polarized currents, and by the same token, the promise of electrical control of magnetic effects. While in some magnetic semiconductors, for example, magnetite, all of the material’s constituent ions are intrinsically magnetic (  concentrated magnets  ), the most recent focus has been on nonmagnetic semiconductor host materials that can be doped by a small amount of magnetic transition-metal ions or by defects that promote magnetism (  dilute magnets  ).

Understanding behavioural patterns: why bird flocks move in unison

Animal flocks, be it honeybees, fish, ants or birds, often move in surprising synchronicity and seemingly make unanimous decisions at a moment’s notice, a phenomenon which has remained puzzling to many researchers.

New research published today in the New Journal of Physics ( co-owned by the Institute of Physics and German Physical Society ), uses a particle model to explain the collective decision making process of flocks of birds landing on foraging flights.

Using a simple self-propelled particle (SPP) system, which sees the birds represented by particles with such parameters as position and velocity, the researchers from Budapest, Hungary, find that the collective switching from the flying to the landing state overrides the individual landing intentions of each bird.

Quantum Time Machine Lets You Travel to the Past Without Fear of Grandfather Paradox

Looking to build a time machine but nervous about the classic grandfather paradox, aka the Marty McFly conundrum, aka the idea that you might unwittingly do something that causes you to never exist in the first place? An MIT professor and a few of his quantum quoting buddies have published a theory that  allows for time travel while circumventing the grandfather paradox . All you need is a quantum teleportation device and a precise understanding of the idea of postselection--Flux Capacitor optional.

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. 

Could some entangled states be useless for quantum cryptography ?

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One of the widely accepted properties of quantum entanglement is secrecy. Since scientists and researchers began working with quantum key distribution, entanglement has been considered an essential part of keeping communications private. What if entanglement didn't always mean secrecy, though ? New work is shedding light on the nature of entanglement and quantum key distribution -  and possibly proving that a high degree of entanglement does not necessarily lead to complete secrecy .

Physicists build quantum amplifier with single artificial atom

By demonstrating how a single artificial atom can be used to amplify electromagnetic waves, physicists from Japan are opening up new possibilities for quantum amplifiers, which can be used in a variety of electronic and optical applications.

Entropy study suggests Pictish symbols likely were part of a written language

How can you tell the difference between random pictures and an ancient, symbol-based language ?

 A new study has shown that concepts in entropy can be used to measure the degree of repetitiveness in Pictish symbols from the Dark Ages, with the results suggesting that the inscriptions appear be much closer to a modern written language than to random symbols 

. The Picts, a group of Celtic tribes that lived in Scotland from around the 4th-9th centuries AD, left behind only a few hundred stones expertly carved with symbols. Although the symbols appear to convey information, it has so far been impossible to prove that this small sample of symbols represents a written language.

Physicsts reveal how to cope with 'frustration'

For most people, frustration is a condition to be avoided. But for scientists studying certain "frustrated" ensembles of interacting components -that is, those which cannot settle into a state that minimizes each interaction-

 it may be the key to understanding a host of puzzling phenomena that affect systems from neural networks and social structures to protein folding and magnetism.

Global classical solutions of the Boltzmann equation with long-range interactions

Ludwig Boltzmann
1844-1906

This is a brief announcement of our recent proof of global existence and rapid decay to equilibrium of classical solutions to the Boltzmann equation without any angular cutoff, that is, for long-range interactions. We consider perturbations of the Maxwellian equilibrium states and include the physical cross-sections arising from an inverse-power intermolecular potential r ^-(p-1) with p > 2, and more generally. We present here a mathematical framework for unique global in time solutions for all of these potentials.  We consider it remarkable that this equation, derived by Boltzmann in 1872 and Maxwell in 1867, grants a basic example where a range of geometric fractional derivatives occur in a physical model of the natural world . Our methods provide a new understanding of the effects due to grazing collisions.

http://www.pnas.org/content/107/13/5744.abstract?sid=9d675b61-b4d1-4bc0-88d1-b450d0b4b5ca
 
Philip T. Gressman and Robert M. Strain
University of Pennsylvania, Department of Mathematics, Philadelphia, PA 19104-6395

Graphene transistor could advance nanodevices

For years, scientists and researchers have been looking into the properties of carbon nanotubes and graphene for use in nanoelectronics.  There is no real mass application of devices based on graphene and carbon nanotubes , Zhenxing Wang tells PhysOrg.com.  This is really an opportunity for them to show their capabilities .

Appl. Phys. Lett. 96, 173104 ( 2010 )

Laser technology provides a quantum leap (La tecnología láser da un salto cuántico)

En la Universidad de Innsbruck ( Austria ), un equipo de investigación financiado con fondos comunitarios ha creado un láser de átomo único que se rige por el mismo principio que los láseres clásicos pero que además presenta propiedades cuánticas en sus interacciones entre átomos y fotones. Los resultados de su investigación, publicados en la revista Nature Physics, ampliarán el conocimiento que se posee de las propiedades de los láseres y podrán utilizarse para medir composiciones de oligoelementos gaseosos e isótopos de carbono en el aire y el suelo.

At the University of Innsbruck ( Austria ), a team of private funded research has created a single atom laser which is governed by the same principle as lasers but also presents classical quantum properties in interactions between atoms and photons. The results of their research, published in the journal Nature Physics, expand the knowledge of the lasers properties and may be used to measure gas compositions of trace elements and isotopes of carbon in the air and soil.

Buscan crear super computadoras sin límite de velocidad

Un equipo de investigadores liderados por científicos de la Universidad de Yale ejecutó exitosamente operaciones simples de mecánica cuántica, lo cual podría significar la creación de hardware con potencial ilimitado de procesamiento.

Synthetic magnetism achieved by optical methods: Technique enables unprecedented insights

For the first time, physicists have used laser light to create  synthetic magnetism , an exotic condition in which neutral atoms suddenly begin to behave as if they were charged particles interacting with a magnetic field -- even though no such field is present and the atoms have no charge. The achievement provides unprecedented insights into fundamental physics and the behavior of quantum objects, and opens up entirely new ways to study the nature of condensed-matter systems that were barely imaginable before.

Stephen Wolfram: The Man Who Cracked The Code to Everything ...

..."The climax of the book is the principle of computational equivalence, which may as well be called "Wolfram's law." After hundreds of pages of laying groundwork, presenting case after case of visual examples where simple rules generate counterintuitively complex results, Wolfram concludes that this phenomenon is overwhelmingly commonplace - it's at the base of everything from morphology to traffic jams. Then he goes further, stating that once a system achieves a certain, easily attainable degree of complexity, it's reached the point of maximum complexity, as measured by the computation required to crank out the end result. Everything at that level of complexity - and that means almost everything you can think of, from human thought to rain hitting pavement - is exactly as complex as anything else."...

String theory pioneer succeeds Hawking in Lucasian role

One of the founders of string theory has been elected to replace Stephen Hawking as Cambridge University's Lucasian Professor of Mathematics. Professor Michael Green becomes the 18th holder of the professorship. Prof Green, who currently holds the John Humphrey Plummer Professorship of Theoretical Physics is one of the founders of string theory, generally regarded as the most successful candidate to date to unify quantum theory and general relativity, the two fundamental physical theories of the early twentieth century, and thereby formulate a consistent quantum theory of gravity.

Deconstructing the electron

Explaining the behavior of interacting electrons in a solid is one of the long-standing problems in condensed matter. For most systems, the problem has been masterfully addressed by Landau, who showed that even though interactions can be very large, excitations behaving essentially as free fermions still exist in the system. The Landau Fermi-liquid theory allows sweeping the interactions under the rug and saying that the properties of many materials will be very similar to those of free electrons. However, this theory fails spectacularly when an electron gas is confined to one dimension. In that case, a completely new universality class appears, and the Fermi liquid turns into a Luttinger liquid.

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