cooper pairs in superconductors

[Jamie M]

Hi,

I was reading that in superconductors electrons form "cooper pairs" with
a net magnetic charge of zero. I was wondering what happens
to these electrons when they accelerate, do they radiate like normal
electrons or will the radiation cancel out and not radiate, ie. in
this case a superconducting "antenna" would not radiate anything.

Or does the zero net magnetic charge only apply to DC current losses?

cheers,
Jamie

 

[Tim Williams]

I don't think cyclotron radiation is a useful mechanism of radiation in
conductors.

Superconductors are lossy at AC. Flux pinning in HTSCs is one example
(hysteretic loss, I suppose). LTSCs can still achieve high Q factors
(e.g., 3 x 10^7 for properly prepared Nb resonators at 4 K -- better than
quartz crystals), but weird surface effects make subtle differences (IIRC,
a polished surface is good, but not actually the best).

Note also that the phenomenon has a fundamental frequency limit, hence why
HTSCs don't suddenly turn from black to silver at Tc.

Tim

 

[Phil Allison]

"Tim Wescott"

A particle with a magnetic charge would be a magnetic monopole. They
exist in some obsolete versions of the standard model, but have (IIRC)
been proven to be impossible in a universe that has electric monopoles
(i.e., electrically charged particles).

Cooper (with a capital C -- they're named after Leon Cooper)

** I'm sure glad it wasn't Sheldon Cooper .......

pairs are
pairs of electrons with opposite spin; the sum of the spin in the two
electrons is zero, which means that the pair makes a boson. That boson
still has a charge, and it still moves around, so it's still going to
induce a magnetic field according to Ampere's law.

** But that guy didn't know thing about Quantum physics - way back in 1826
!!

Nor did he know the speed of light with any great accuracy OR that it was
invariant between observers.

Just got lucky I guess.............

That doesn't have anything to do with the spins of the electrons involved.

** Back in my last high school days, some smart arse physics dude informed
me that practically the whole of Chemistry (ie chemical bonding) derived
from the Z component of the spin of the electron.

True or not ?


..... Phil

 

[boB]

A particle with a magnetic charge would be a magnetic monopole. They
exist in some obsolete versions of the standard model, but have (IIRC)
been proven to be impossible in a universe that has electric monopoles
(i.e., electrically charged particles).

Cooper (with a capital C -- they're named after Leon Cooper) pairs are

LC ( was he resonant ?)

But we don't capitalize watt as in 10.3 watts.... Only when the
single letter is used, llike, 10.3 W or kW or dB or whatever...

Are the rules different for things like this, as in Cooper pairs, etc
? Only really important to me if I'm working on a manual or something
where I don't want to look too stooopid if I can help it.

 

[Tim Williams]

LC ( was he resonant ?)

But we don't capitalize watt as in 10.3 watts.... Only when the
single letter is used, llike, 10.3 W or kW or dB or whatever...

Are the rules different for things like this, as in Cooper pairs, etc
?

Yes.


(...) Named phenomena are capitalized (e.g., Cooper pairs, Hoffman
addition...), units are lowercase (not Proper Nouns) or abbreviated (in
which case the symbols are used, e.g., tesla = T).

Tim

 

[Jamie M]

A particle with a magnetic charge would be a magnetic monopole. They
exist in some obsolete versions of the standard model, but have (IIRC)
been proven to be impossible in a universe that has electric monopoles
(i.e., electrically charged particles).

Hi,

A Cooper pair isn't a particle is a pair of particles, so could have a
zero net magnetic charge without being a monopole.

Cooper (with a capital C -- they're named after Leon Cooper) pairs are
pairs of electrons with opposite spin; the sum of the spin in the two
electrons is zero, which means that the pair makes a boson. That boson
still has a charge, and it still moves around, so it's still going to
induce a magnetic field according to Ampere's law. That doesn't have
anything to do with the spins of the electrons involved.

I think the magnetic field comes from the spin, so if the spins cancel
their should be no field. I guess under acceleration things get
different, and maybe the Cooper pair charge becomes non-zero.

cheers,
Jamie

 

[George Herold]

exist in some obsolete versions of the standard model, but have (IIRC)
been proven to be impossible in a universe that has electric monopoles
(i.e., electrically charged particles).

No, there can still be magnetic monopoles. There is a proof by (Dirac?) that if one magnetic monopole existed it would explain charge quantization. (Something to do with conservation of angular momentum I think.) (My pet theory is that magnetic monopoles exist.. but they are tightly bound up into magnetic 'atoms'.)

George H.

 

[George Herold]

"Tim Wescott"

** Back in my last high school days, some smart arse physics dude informed
me that practically the whole of Chemistry (ie chemical bonding) derived
from the Z component of the spin of the electron.

No. Hmm, Well OK if by spin he just meant that electrons have spin 1/2 andthat means they can't be in the same state. Electrons in atoms can have different amounts of angular momentum along the z-axis, but that doesn't effect the chemistry very much.. which is why I first wrote no. Most of chemistry is how the outer electrons bond.. (get together.)

George H.

 

[Tim Williams]

No. Hmm, Well OK if by spin he just meant that electrons have spin 1/2
and
that means they can't be in the same state. Electrons in atoms can have
different amounts of angular momentum along the z-axis, but that doesn't
effect the chemistry very much.. which is why I first wrote no. Most of
chemistry is how the outer electrons bond.. (get together.)

Z component, sure, but how does one then explain the *other four* orbitals
that hold together the 99.99973% of chemistry? ;-)

But really, the only part about spin that affects everyday chemistry is it
allows electrons to double up (if unwillingly). Molecules with single
electron bonds exist, e.g., H2(+). Without spin pairing, it would be a
very different universe, of course (not the least of which because all of
QM would have to be torn up and rewritten..).

Tim

 

[[email protected]]

I was reading that in superconductors electrons form "cooper pairs" with
a net magnetic charge of zero. I was wondering what happens
to these electrons when they accelerate, do they radiate like normal
electrons or will the radiation cancel out and not radiate, ie. in

I'm not sure I understand what you're after ... not only
Cooper pairs but also rest of the (observed) material in
the world has zero magnetic charge. It is accelerated *electric*
charge which radiates. Accelerated Cooper pairs, being
electrically charged, do radiate.

Regards,
Mikko

 

[George Herold]

Z component, sure, but how does one then explain the *other four* orbitals

that hold together the 99.99973% of chemistry? ;-)

But really, the only part about spin that affects everyday chemistry is it
allows electrons to double up (if unwillingly). Molecules with single
electron bonds exist, e.g., H2(+). Without spin pairing, it would be a
very different universe, of course (not the least of which because all of

QM would have to be torn up and rewritten..).

One of pet peeves is when people say the atom is empty. All this free space. There's no damn free space it's all full of electrons!
My butt doesn't go through my seat cushion, because of the electrons.
They think that because the electron is light it doesn't take up much space.. completely backwards. (I rant at my kids when this type of talk comes home from school. Their response is to roll their eyes.. there goes Dad again. :^)
kids, they keep you humble.

George H.

 

[Martin Brown]

One of pet peeves is when people say the atom is empty. All this free space. There's no damn free space it's all full of electrons!

Full isn't really a helpful description. You are imagining something
like the plum pudding model of the atom that was comprehensively
disproved by Rutherfords backscattered alpha particles.

It is correct to a very good approximation to say that the atom is more
or less empty. But that there is an outer surface that due to like
charges repelling behaves as if it is extremely tough.

White dwarf matter held up soley by electron degeneracy pressure is
dense and in a neutron star the matter is truly nuclear dense. There is
a conjecture that certain repeat supernovae recently observed have
condensed into an even denser state of matter nominally a quark star.

http://arxiv.org/abs/1308.3927v1

The jury is still out on this one...

My butt doesn't go through my seat cushion, because of the electrons.
They think that because the electron is light it doesn't take up much space.. completely backwards. (I rant at my kids when this type of talk comes home from school. Their response is to roll their eyes.. there goes Dad again. :^)
kids, they keep you humble.

George H.

Whenever you try to look for an electron then it is tiny, but in the
context of an atom they are neatly smeared out across space and time in
a manner consistent with Schrodinger's equation (or rather its
relativistic cousin the Dirac equation). The wavefunction amplitude
tells you how likely you are to see it in a particular position.

 

[George Herold]

Full isn't really a helpful description. You are imagining something
like the plum pudding model of the atom that was comprehensively
disproved by Rutherfords backscattered alpha particles.

Huh? No I'm not! The plum pudding model had little electrons in a sea of positive charge.

It is correct to a very good approximation to say that the atom is more
or less empty. But that there is an outer surface that due to like
charges repelling behaves as if it is extremely tough.

OK, I've had this discussion before with other physicists. It's not repulsive charges that keeps electrons from one atom out of the other. It's the Pauli exclusion principle. (electrons are spin 1/2 fermions.)

If you want to talk about blasting high energy particles through atoms thenI guess I don't care if you call it mostly empty or not. But that's *not*how we typically deal with atoms every day. The atom is totally full withelectrons when it comes to touching it with another electron.. like the ones in the atoms on the end of your finger.

White dwarf matter held up soley by electron degeneracy pressure is

Hmm I'm not very current on my astronomy/ stellar physics. But in a white dwarf aren't the electrons stripped from the atoms? There's enough energy so that everyone is ionized. Again not a very common place example. So let's stick with atoms.

I'm not going to have the patience (or time) to show you that repulsive charge is not at work in atom to atom repulsion. (or not the dominate cause.)I could try an appeal to authority... but that's not very satisfying either. Maybe I can just ask you to read and think about it. I'm sorta 90% sure I've got a decent picture of how it works. And this is a perhaps a chance for you to make a 'tweak' to your model of the universe. (I hope that doesn't sound condescending. I get the feeling you're much smarter than I am.) When I try and think more deeply about it... how do the electron orbitals distort when atoms are pushed together.. and what exactly is the "state" of this distorted outer shell electron.. it all gets confusing.

Light things take up more space in QM than heavy things. That is not something people find easy to understand.

George H.