electron- electron attraction

[Ankit Gupta]

We all know that a proton binds to another proton through strong nuclear force but do also an electron binds to another , I haven't heard that there for asked ?

[studiot]

Not directly, but you could regard the pairing of two electrons in an orbital, thereby lowering their combined system energy, as a form of attraction.

[Ankit Gupta]

But we cannot take it as a binding electrons even they were not attracting also but why do two electrons cannot bind like to protons

[studiot]

 

But we cannot take it as a binding electrons even they were not attracting also but why do two electrons cannot bind like to protons

 

 

I have no idea what this means.

[swansont]

Electrons don't bind like protons because they don't interact in a way that allows it. Protons interact via the strong interaction, electrons via the weak, in addition to the electromagnetic.

[MigL]

Technically protons don't bind to other protons.

The quarks making up the protons bind via the strong interaction ( QCD) and some 'residual' interaction binds the quark-containing-protons together.

This only happens when a given separation is reached. At greater separation protons repel just like electrons since EM force is dominant.

Edited December 4, 2013 by MigL

[Enthalpy]

Not directly, but you could regard the pairing of two electrons in an orbital, thereby lowering their combined system energy, as a form of attraction.

Very indirect then. The magnetic attraction from pairing is faint, similar to the fine structure. The big effect - the chemical bond - results from putting both electrons on the favoured orbital.

[Ankit Gupta]

Technically protons don't bind to other protons.

The quarks making up the protons bind via the strong interaction ( QCD) and some 'residual' interaction binds the quark-containing-protons together.

This only happens when a given separation is reached. At greater separation protons repel just like electrons since EM force is dominant.

QCD ?

[swansont]

Quantum ChromoDynamics

[Ankit Gupta]

Quantum ChromoDynamics

and what is it ?

[swansont]

http://en.wikipedia.org/wiki/Quantum_chromodynamics

[hoola]

electrons can pair up in a superconductor into what are called "cooper pairs".....but only at very low temperatures. For some reason, the pairing of electrons seems to cause electricity to flow through a conductor with no resistance.....and expell it's magnetic field in the process....edd

[Ankit Gupta]

electrons can pair up in a superconductor into what are called "cooper pairs".....but only at very low temperatures. For some reason, the pairing of electrons seems to cause electricity to flow through a conductor with no resistance.....and expell it's magnetic field in the process....edd

would u please explain cooper loop more I tried it on internet but didn't understand

[Enthalpy]

Cooper pair: search for BCS theory.

 

In BCS, electrons are said to pair because they deform the crystal. Some sort of pairing is to be more favourable, in combination with the deformation. No idea how this relates with spin.

[MigL]

Electrons are fermions and as such, obey Fermi-Dirac statistics.

I always assumed ( ie I'm probably wrong ) that they paired up in superconductors, such that spins are additive.

The paired 'particle' is then equivalent to a spin 1 boson and can follow the rules of Bose-Einstein statistics.

[Enthalpy]

Nearly all electrons are already paired in a metal at room temperature. So are they in a plastic, a ceramic...

Though, these materials are not superconductors, so the usual short explanation is just too short.

Anyway, I don't see neither why a boson would travel unhindered.

[swansont]

Nearly all electrons are already paired in a metal at room temperature. So are they in a plastic, a ceramic...

Though, these materials are not superconductors, so the usual short explanation is just too short.

Anyway, I don't see neither why a boson would travel unhindered.

 

No, they aren't, in the way Cooper pairs exist.

 

Bosons interact differently, since there is no restriction on them having to occupy different quantum states. Thus they can all be in a ground state of a potential, and in that state, they can't lose energy.

[MigL]

My thinking also, swansont.

[Enthalpy]

I maintain electrons are paired in most materials. I just want to point out that the usual "paired hence boson hence condensed" is too short an explanation. There must be something else in Cooper pairs.

 

Cooper pairs can't neither be all in ground state. As electrons in a metal have 5-10eV energy above the lowest available state, the transition would give hugely more heat than is observed. And anyway, several electron pairs in any material don't occupy the ground state: not in an atom, not in a molecule, not in a metal.

 

Two fermions can occupy the same state, say an orbital. Other pairs, despite being bosons, can't occupy the same state.

 

The BCS theory is certainly something else.

Edited December 13, 2013 by Enthalpy

[swansont]

Two fermion cannot occupy the same state in an atom. They must have some quantum property that is different. Energy, orbital angular momentum, or spin orientation (n,l,m).

 

Electrons in a conductor are not 5-10 eV above any available state; the valence band, below the conduction band, is full, and overlaps with the conduction band, so the electrons are free to move around. What you say may be true for semiconductors, where the electrons must be promoted to the conduction band.

 

As I understand it, the Cooper pairs are in a specific bound state potential. Within that potential, they are in the ground state. If the system heats up, that confining potential is destroyed and it's no longer a superconductor. I don't know what pairing exists that you're talking about.

[Enthalpy]

Happy to see that you agree with me.

 

The electrons, even paired, cannot occupy the ground state 5-10eV below, because the bands are full and the exclusion principle applies - so no bizarre story of behaving like bosons.

 

Electrons grouping in pairs, including thoses electrons near the Fermi level, is a part of standard BCS theory. This pairing is to result from lattice deformation.

 

I want to distinguish such a pairing from spin pairing on an available state, which does not make a superconductor, and does not permit electron nor pairs to occupy the same state. BCS explanation of superconductivity does not rely on standard spin pairing.

[swansont]

Happy to see that you agree with me.

 

The electrons, even paired, cannot occupy the ground state 5-10eV below, because the bands are full and the exclusion principle applies - so no bizarre story of behaving like bosons.

 

Electrons grouping in pairs, including thoses electrons near the Fermi level, is a part of standard BCS theory. This pairing is to result from lattice deformation.

 

I want to distinguish such a pairing from spin pairing on an available state, which does not make a superconductor, and does not permit electron nor pairs to occupy the same state. BCS explanation of superconductivity does not rely on standard spin pairing.

 

I can't agree with you because you're talking about something different from what I am talking about.

 

There is no ground state 5-10 eV below; the band structure is a separate issue here. The potential that allow the electrons to pair is a different — it's due to lattice vibrations. They are two separate things. Within the potential that allows the electrons to be bound to each other, the Cooper pairs are in the ground state. The Cooper pairs do indeed act like bosons.

 

"these coupled electrons can take the character of a boson and condense into the ground state."

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/coop.html

 

http://en.wikipedia.org/wiki/BCS_theory

[Enthalpy]

You can't put several electron pairs into a single state, because electrons are fermions. However they're "paired".

 

Anyway, electrons, or pairs, or many pairs, in the ground state, would not move, hence no current.

 

Maybe I should read the BCS theory some day. It must differ seriously from the explanations given usually, includung at Hyperphysics and Wiki. I know this kind of interpretations, and believe the interpretations are wrong.

[swansont]

You can't put several electron pairs into a single state, because electrons are fermions. However they're "paired".

 

Two bound spin 1/2 particles in a system has integral spin and is then a composite boson. Perhaps you've heard of Bose-Einstein condensates? Those are atomic systems that are composite bosons, that have condensed into the ground state of the confining potential. It was a pretty big deal, winning the Nobel in 2001. BCS theory was also a big deal and won in 1972.

 

So yes, they do, and it's been experimentally confirmed for some time now.

 

Anyway, electrons, or pairs, or many pairs, in the ground state, would not move, hence no current.

 

Ground state does not mean no energy.

 

Maybe I should read the BCS theory some day.

That would be a better option than spouting off on it without having learned about it.

 

[Enthalpy]

So yes, they do, and it's been experimentally confirmed for some time now.

 

What experiments say is that

- There is a condensation energy

- The quantum flux shows TWO electrons together, not 10²³

 

They don't say that ALL electrons are in the same state. Maybe they don't even tell that the paired electrons are of opposite spin, nor even in the same state except for spin: some reports tell that the paired electrons have opposite momentums, which then doesn't need paired spins.

 

Ground state does not mean no energy.

 

But ONE ground state does mean no movement. Movement and acceleration need a change of state. And energy does not mean quantity of movement.

 

That would be a better option than spouting off on it without having learned about it.

 

Cool down! BCS is known not to work for higher temperature superconductors. And what I see everywhere, be it on Wiki; Hyperphysics, or the ideas here gained there, is not BCS, with a very high probability. So defending things like "bosons all in the same state" is not necessarily defending BCS.