The ferromagnetic Kondo effect

Jul 24, 2013

A group of physicists that includes scientists of the International School for Advanced Studies (SISSA) of Trieste have shown how to obtain a particular case of a physical effect – so far never observed in reality – whose studies have earned a Nobel Prize. The scientists have also observed the response of the material subject to such effect. These observations will provide precious indications to the experimental physicists in order to verify, in the future, their theory.

The Kondo effect in 1982 earned the Nobel Prize in Physics to Kenneth Wilson – the American physicist who passed away this year – who had solved numerically such solid-state physics "problem". Now a group of scientists, including some researchers of the International School for Advanced Studies (SISSA) of Trieste have explored a lesser known variant, predicting theoretically that the phenomenon can be actually observed, and describing its behavior in detail.

The Kondo effect, described for the first time in the last century by Japanese physicist Jun Kondo, is observed when a magnetic is added to metals such as gold or copper, that is, very few atoms (in some cases even only 1 out of 1,000) of a such as iron.

"Each electron features a moment, both of rotation and magnetic, called spin. Kondo is a phenomenon linked to the spin of metal electrons," explains Erio Tosatti, a scientist of SISSA and one of the authors of the paper just published in Physical Review Letters. "The free metal electrons surround the impurity like a cloud and arrange themselves into a spin that screens out the impurity, to a point that it is not detectable any longer, at least as long the temperature is sufficiently low. This affects selected properties of the materials, such as an increase in and in the resistance to the flow of electrons in the metal. "

More in detail…

Tosatti, who also collaborates with ICTP and Laboratorio Nazionale Democritos of Istituto CNR-IOM, has joined forces with Michele Fabrizio and Ryan Requist of SISSA, and Paolo Baruselli, a former student of SISSA now at Dresden University of Technology. The team has studied a particular case, that is, the"ferromagnetic Kondo effect." In this case the metal electrons will align their spins in a way that does not screen out those of the electrons of the iron atoms, but instead "anti-screens" them, preserving their magnetism. Compared to the traditional Kondo effect, this will change the resistivity properties of the material. Tosatti and his colleagues have now proposed and described a circuit, made up of three quantum dots ("puddles" of electrons trapped inside a semiconductor), where, by simply adjusting a parameter, both the ferromagnetic and the ordinary Kondo effects may be observed, distinguished by their different and opposed electrical conduction anomalies .

Now the phenomenon has to be verified. "We expect" concludes Tosatti, "that our experimental colleagues will now try to reproduce the same conditions we have indicated in order to carry out what could be the first observation of a phenomenon that has been theorized for a long time but never verified so far".

Explore further: How do cold ions slide

More information: Phys. Rev. Lett. 111, 047201 (2013) DOI: 10.1103/PhysRevLett.111.047201

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vacuum-mechanics
1 / 5 (6) Jul 25, 2013
"Each electron features a moment, both of rotation and magnetic, called spin. Kondo is a phenomenon linked to the spin of metal electrons," explains Erio Tosatti, a scientist of SISSA and one of the authors of the paper just published in Physical Review Letters. "The free metal electrons surround the impurity like a cloud and arrange themselves into a spin that screens out the impurity, …


Unfortunately we do not know why and how the moving electron could rotate and create the magnetic field, understand its working mechanism would help the research…
http://www.vacuum...=4〈=en
antialias_physorg
not rated yet Jul 25, 2013
Unfortunately we do not know why and how the moving electron could rotate and create the magnetic field


First understanding that the lable 'spin' - as applied to elementary particles - does not denote a rotation at all (much like a 'color charge' in quantum chromodynamics does not mean that these objects are actually green or red or blue) may help to clear up your confusion about these things.

http://en.wikiped...ysics%29

antialias_physorg
not rated yet Jul 25, 2013
Read the first part of the link:

Spin is a solely quantum-mechanical phenomenon; it does not have a counterpart in classical mechanics (despite the term spin being reminiscent of classical phenomena such as a planet spinning on its axis)

an this part

- Spin quantum numbers may take half-integer values.
- Although the direction of its spin can be changed, an elementary particle cannot be made to spin faster or slower.
- The spin of a charged particle is associated with a magnetic dipole moment with a g-factor differing from 1. This could only occur classically if the internal charge of the particle were distributed differently from its mass.


The name 'spin' was used BECAUSE it maps mathematically to quantized angular momenta. Not because anything is rotating.

'Spin' is a label like 'wave particle' (which doesn't mean the thing is a wave or a particle. It only means it has some properties that map onto those of waves and particles. )

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