Spin-Charge separation seem to have been experimented

[microsansfil]

Hello,

There this article "http://www.nature.com/nphys/journal/v11/n1/full/nphys3172.html".

High-energy experiments have shown that the electron is a point-like particle with spin-1/2 and electric charge -e. In highly correlated condensed matter systems these two properties can decouple in the lowest level excitations with the creation of two new quasiparticles: spinons (which carry spin) and chargons (which carry electric charge).

What are the fondamental difference between these "quasi-particles" and the particles with properties of spin and charge ?

Patrick

 

[Vanadium 50]

I'm not sure how much you will get from the article without knowing the basics. Have you started with Wikipedia? http://en.wikipedia.org/wiki/Spin–charge_separation Is that clear, too basic or too advanced?

 

[microsansfil]

I'm not sure how much you will get from the article without knowing the basics. Have you started with Wikipedia? http://en.wikipedia.org/wiki/Spin–charge_separation Is that clear, too basic or too advanced?

Ok Thank,

Like physical particles, quasiparticles seem have properties such as mass, spin, charge, momentum, etc.

More precicely, do we have the same power of prediction with this concept of quasiparticles than with the concept of particles ("real" particles) ?

Can they and do affect the physics and dynamics of the systems in which they arise ?

Patrick

 

[Vanadium 50]

The fact that you posted this in HEP, and that you didn't answer my question implies that you don't know what quasiparticles are. In condensed matter systems we have collective motion of particles, and it is sometimes mathematically possible and convenient to instead treat this as motions of fictitious particles (quasiparticles) in free space. You might again start with Wikipedia http://en.wikipedia.org/wiki/Quasiparticle and tell us if this is too simple, too advanced or just right but there's still something you don't understand.

 

[microsansfil]

you don't know what quasiparticles are.

Yes. It is partly my question. What are the usefulness of quasiparticles ?

You might again start with Wikipedia http://en.wikipedia.org/wiki/Quasiparticle and tell us if this is too simple, too advanced or just right but there's still something you don't understand.

I only want to know if this concept of quasiparticle is needful to do physical prediction or it is just a mathematical artifice without physical meaning ?

In other words. In what this "tool" is useful for a physicist experimenter ?

What about that don't you get in my question ?!

Patrick

 

[mfb]

Yes. It is partly my question. What are the usefulness of quasiparticles ?

They are good descriptions in many complex systems, and they share many properties with real particles. It is complicated to describe the combined motion of 10^30 atoms, but a description of quasiparticles (here: phonons) moving through the solid is much easier.

I only want to know if this concept of quasiparticle is needful to do physical prediction or it is just a mathematical artifice without physical meaning ?

It is not necessary, but it makes physics much easier.

 

[microsansfil]

They are good descriptions in many complex systems, and they share many properties with real particles. It is complicated to describe the combined motion of 10^30 atoms, but a description of quasiparticles (here: phonons) moving through the solid is much easier.
It is not necessary, but it makes physics much easier.

Thank. Thus spin-charge separation is not a physical phenomenon ?

Patrick

 

[mfb]

What do you call "physical phenomenon"?
Is sound a "physical phenomenon"? In solids, it gets described with quasiparticles.

 

[microsansfil]

What do you call "physical phenomenon"?

For example particles, interactions which have physical properties.

Is sound a "physical phenomenon"? In solids, it gets described with quasiparticles.

Thus quasiparticles is more than only mathematical concept ? Can quasiparticles be experimented like particles ?

Are the spinon and the chargons physical properties like spin and electric charge ?

We can read on the wiki :

http://en.wikipedia.org/wiki/Spin–charge_separation

In condensed matter physics, spin–charge separation is an unusual behavior of electrons in some materials in which they 'split' into three independent particles, the spinon, orbiton and the chargon (or its antiparticle, the holon). The electron can always be theoretically considered as a bound state of the three, with the spinon carrying the spin of the electron, the orbiton carrying the orbital degree of freedom and the chargon carrying the charge, but in certain conditions they can become deconfined and behave as independent particles.

What is the meaning of : spinon carrying the spin of the electron ?

Patrick

 

[mfb]

For example particles, interactions which have physical properties.

What are physical properties? What are particles?
This is becoming philosophy. Physics does not describe how the world "really is". It gives tools to describe the results of experiments. Particles like the electron are a tool, quasiparticles like phonons are another tool. Both work nicely.

Thus quasiparticles is more than only mathematical concept ?

It is a concept of physics.

Are the Spinon and the chargons physical properties like spin and electric charge ?

Quasiparticles are not physical properties, they have physical properties (like spin and charge).

 

[microsansfil]

This is becoming philosophy. Physics does not describe how the world "really is".

It is not my question. It's complicated enough without adding philosophy.

It gives tools to describe the results of experiments. Particles like the electron are a tool, quasiparticles like phonons are another tool. Both work nicely.
It is a concept of physics.

It is my question. I can understand this.

Quasiparticles are not physical properties, they have physical properties (like spin and charge).

Thus it is a physical concept to speak about the behavior of an electron in the context of condensed matter system ?

Patrick

 

[mfb]

Thus it is a physical concept to speak about the behavior of an electron in the context of condensed matter system ?

Sure.

 

[microsansfil]

Hello,

I found this article : http://www.london-nano.com/research...magnetic-quasi-particles-in-a-two-dimensional

Electrons carry both a charge and a magnetic moment, and the collective way in which electrons behave leads to the familiar electrical and magnetic properties of materials. Isolated electrons are fundamental particles, in the sense that they are believed to be indivisible into smaller entities. Electrons in an interacting system, on the other hand, take on a different guise, becoming quasi-particles, which in certain circumstances are believed to break up, or fractionalise, into new types of quasi-particle.

The most extreme form of quasi-particle fractionalisation is observed in one-dimensional conductors, where the magnetic and electrical properties of the electron quasi-particles part company completely, exhibiting a phenomenon known as spin-charge separation. While it is known that fractionalisation can also occur in higher dimensions – as, for example, in the quantum Hall effect – observing such phenomena particularly in magnetic systems has proven to be elusive.

An international team of scientists from Switzerland, the USA, France, Denmark and Britain, including members from the LCN, recently reported in Nature Physics the observation of fractionalisation in a two-dimensional quantum magnet. Their study combined state-of-the-art polarized neutron scattering techniques with a new theoretical framework. This allowed them to establish definitively that the magnetic quasi-particles, known as magnons, split into two halves (‘spinons’), that move independently of one another, at specific energies and along specific directions in the material - See more at: http://www.london-nano.com/research...les-in-a-two-dimensional#sthash.RRiONDrJ.dpuf

Patrick

 

[cgk]

microsansfil, quasi-particles are a way of describing the complex motion of many individual, interacting "real" particles in an effective way, which makes it easier to see what is going on. There are both real-life and physical analogs of that. For example, when police observes a demonstration in real life, they might describe it as a crowd of 1000 people moving through street X, instead of keeping track of 1000 individual persons. The motion of the crowd is ultimately determined by the behavior of individuals and their environment and interactions, but in most cases it will not be required to understand the detailed intentions and movements of every individual to make sense of the movement of the crowd---so a person just becomes one effective crowd-participant (a quasi-individual?) for the sake of tracking the overall demonstration.

A better analogy might be found in electronics. There one is not normally concerned with the motion of individual electrons through wires; instead, one makes up the concept of a "current" of effective charge carriers, and combined with Ohm's law (which is really a highly non-trivial approximation!), it allows for deriving many properties of the resulting material. Note that the effective charge carriers in metals are not the electrons either (they move much slower than electrons!).

Now, like in the electric current and Ohm's law example, there are many cases where such an effective description works fine. But there are also cases where the actual microscopic nature of the motion shines through and deviations from the effective laws start to appear. If this happens, this is generally considered as an interesting physical effect. What we see in the article you posted is one such case. The real spin and real charge still sit with the electrons, but due to their interacting motions in a complex environment, we get an effective description where those degrees of freedom are better described as being separated.
If you now ask the question if quasi-particles are real: they should probably be considered as real, but they are not elementary physical objects (i.e., they arise from an effective description of the very complex interacting motion of the "real" physical electrons). Your question is thus similar to asking whether "a crowd" is real, or if there are really only 1000 individual people. This is what mfb meant by saying that this becomes philosophy.

 

[microsansfil]

Hi cgk,

Thank, I thing that i understand the approach of Local versus global.

Patrick

 

[ZapperZ]

The problem with this thread is that you are trying to run before you learn how to even walk.

The articles you cited are highly advanced, especially when what you should have tried to first learn is the concept of "quasiparticles".

Ironically, both of those articles that point to a possible spin-charge separation, show that the concept of quasiparticles, at least the ones defined under Landau's Fermi Liquid theory, breaks down in those systems! The quasiparticles that we know so much in ordinary metals, semiconductors, etc, can no longer be used in such a system. This is similar to what is expected in a 1D system that is described as a Luttinger liquid.

For your information, there are already at least couple of earlier papers that point to such spin-charge separation based on the violation of the Wiedemann-Franz law (http://physicsworld.com/cws/article/news/2011/jul/27/spinons-take-the-heat), so this is not something new.

To learn the concept of "quasiparticles" and the physics of many-body interactions, I strongly suggest getting the Dover book by Mattuck "A Guide to Feynman Diagrams in the Many-Body Problem" and see for yourself the physics of it and how it is so widely used.

Zz.