Superconductivity at room temperature??

[sol invictus]

In a conductor the charge-carriers flow in order to cancel the applied electric field but it cannot ever be achieved as long as a current is flowing; even when these charge-carriers do not scatter at all. This is exactly what Drude's equation also confirms. So why does the field become cancelled within a superconductor

It's trivial, Johan, but I'm nearly certain you won't understand the explanation, so I don't really have the will to type it out. The bolded assertion is of course false, but when I show you counterexamples you'll just complain that they weren't what you meant and you'll fail to get the physical point they illustrate.

By then postulating that the charge-carriers can magically violate physics by not radiating EM while being accelerated towards the centre of the ring, one can argue that they will coast along indefinitely:

A constant circulating current does not radiate. You've been told this over and over and over, we've explained the physical reason and shown you the mathematics, but you continue to falsely assert the contrary with no evidence and no reasoning. It is useless to discuss it further.

 

[johanfprins]

Comments on post #1138 by Olowkow

My bad. Poorly stated. Ok, sorry, I was not clear enough. Of course, the persistent current is such a case, but I was speaking of the situation of having the source connected.

It was obvious to anybody with common sense what you meant. That sol invictus cannot understand this, is typical of all his responses on this thread: And probably of any posting he/she has ever made. Just ignore him/her as being an irrelevant nuisance.

 

[johanfprins]

Comments on post #1138 by Ben m

What makes you say that? You can put a Josephson junction into a superconducting ring, and induce a persistent loop current through the superconductor AND the junction. This is part of the circuitry of a SQUID magnetometer, for example.

You see what I mean Olowkow? I should also have mentioned Ben m and Ziggurat in my previous posting. Are these three the same person? Or are they just the three S------s

 

[johanfprins]

Comments on post #1140 by Ben m

I think you mean Langenberg, Scalapino, and Taylor in Proc. IEEE[/I] 54 (1966) 560.

Sorry a typing error.

The only part of the curve showing the thin-junction behavior in isolation is the vertical branch on the far left of fig. 3. After that it's showing some more complicated circuit, which isn't even diagrammed because it's not the point of the paper.

And you claimed all along that the circuit cannot affect what one measures! Now you admit that it can! So you have been dishonest?!

The "jump" you're looking at is an artifact of this "switch... along the measuring load line", and is not present in more straightforward circuits.

And you will notice that even after this load-line jump, they still had to increase the voltage before "normal tunneling" started.

Scalapino's paper cites Phys Rev Lett 10 230, which describes the measuring circuit more explicitly; there's no "load line", they give resistor values for the DC current supply and the current-monitoring shunt resistor; and the circuit is (once again) the thing I've been talking about all along.

So in all cases after reaching the maximum current at zero voltage "normal tunneling" immediately kicks in at zero voltage? If that is the case, most text books on superconduction need to be rewritten. In most of them they show a drop in current to zero and then, only after increasing the voltage to a suitable value, does "normal tunneling" initiate. In the paper from Berkeley which you quoted this does not happen in Fig. 2: Why not?

 

[sol invictus]

So in all cases after reaching the maximum current at zero voltage "normal tunneling" immediately kicks in at zero voltage? If that is the case, most text books on superconduction need to be rewritten.

Which textbooks specifically, Johan? You were already asked that and replied with a paper from 1966 that doesn't support your assertion. Care to try again?

 

[ben m]

Sorry a typing error.

And you claimed all along that the circuit cannot affect what one measures! Now you admit that it can! So you have been dishonest?!

Yes, the whole circuit helps determine the behavior of the whole circuit. This is true for Scalapino's circuit and it's true for your N-batteries-and-a-capacitor circuit (I presume this is what you're referring to).

The problem with you circuit analysis is not that you try to "include the capacitor" or some such, when I'd prefer to ignore the capacitor. The problem with your circuit analysis is that you are mis-analyzing the included capacitor.

And you will notice that even after this load-line jump, they still had to increase the voltage before "normal tunneling" started.

Yes, as expected.

So in all cases after reaching the maximum current at zero voltage "normal tunneling" immediately kicks in at zero voltage?

Um. No, "normal tunneling" requires higher voltage. Look at the curve. Where do you see evidence of "normal tunneling" "at zero voltage"?

 

[johanfprins]

Comments on post #1141 by sol invitus

It's trivial, Johan, but I'm nearly certain you won't understand the explanation, so I don't really have the will to type it out. The bolded assertion is of course false, but when I show you counterexamples you'll just complain that they weren't what you meant and you'll fail to get the physical point they illustrate.

A masterful retreat while claiming victory. Not even Saddam Hussain could have done it better after the first Gulf War. Very impressive indeed!

A constant circulating current does not radiate.

In a normal conductor you are correct; but we are not talking about a normal conductors.

You've been told this over and over and over,

And I have told you over and over and over that if there is not a normal current, so that the charge-carriers accelerate to the center of the ring, you will get EM radiation. You get it for any charge that accelerate in the same manner and you have claimed that what one obtains is only determined by the acceleration; but in the next breath you claim consistently that although this is true for any free charge being accelerated it is suddenly not true when a charge accelerates in this identical manner within a superconductor!

 

[johanfprins]

Comments on post #1141 by sol invictus

Which textbooks specifically, Johan? You were already asked that and replied with a paper from 1966 that doesn't support your assertion. Care to try again?

I cannot remember all of the text books I have scanned in libraries; but I have already mentioned Fig. 44-15 in Serway; although it is not a text book on superconduction. Since you asked, I quickly looked on my shelf which is not the best library; but can quote:

Andrei Mourachkine: book published by Cambridge International Science Publishing (see page 48). Although I must agree that what comes from Cambridge on this issue should be distrusted.

D R Tilley and J Tilley: book published by the IOP (see page 264).

I am sure that I can find many more in a scientific library which show that the superconducting current first drops to zero and stays at zero while the voltage is increased until normal superconduction initiates; but I have better things to do.

 

[Ziggurat]

You know quite well that I have never claimed that the polarization of the charge-carriers is sufficient to also cancel the whole applied electric field.

I don't care what cancels the field. The fact remains, the field is canceled. And you HAVE claimed the field is canceled, many times. So regardless of what causes the cancellation of the field, the field is still zero, and so it exerts no force on your dipoles. Any remaining polarization when there is no field (and thus no force from the field) must therefore have no spring constant, or the polarization would drop to zero.

So you agree that zero resistance does not automatically implies zero voltage?

Of course I agree with that. That in fact was one of our points of contention very early in the thread. I stated repeatedly that you could have an electric field inside a superconductor, and you could accelerate charges in a superconductor. Zero resistance and nonzero voltage requires that the current changes over time, but that's fine. That's not a problem. Everything I've said has been consistent with that.

You, however, have not been consistent at all.

But you explain superconduction as if a superconductor is a bare vacuum gap through which charge-carriers can coast at a speed v without having to first do work on them to generate this speed.

No, johan. Work always needs to be done to accelerate any particle from rest, but if a charge carrier moves into a superconductor, guess what? It's already moving. The work can be done external to the superconductor. The relevant difference is that the contact point is not itself a barrier. But the contact point between a cathode and the vacuum gap IS a barrier. That makes a vacuum diode intrinsically different than a superconductor.

 

[sol invictus]

A masterful retreat while claiming victory. Not even Saddam Hussain could have done it better after the first Gulf War. Very impressive indeed!

First Goebbels, now Saddam Hussein. Your paranoia is indeed very impressive.

And I have told you over and over and over that if there is not a normal current, so that the charge-carriers accelerate to the center of the ring, you will get EM radiation.

In a normal (or superconducting, or charges-nailed-to-a-spinning-disk) circulating current the charge carriers of course DO accelerate to the center of the ring, but they do not radiate.

you have claimed that what one obtains is only determined by the acceleration

Yes.

but in the next breath you claim consistently that although this is true for any free charge being accelerated it is suddenly not true when a charge accelerates in this identical manner within a superconductor!

You have failed so many times to comprehend this basic point that I have as much hope left of explaining it to you as I do to my goldfish.

 

[johanfprins]

Comments on post #1146 by Ben m

Yes, the whole circuit helps determine the behavior of the whole circuit. This is true for Scalapino's circuit and it's true for your N-batteries-and-a-capacitor circuit (I presume this is what you're referring to).

So you did lie when you said it makes no difference!!!!!

Yes, as expected.

Oh? Now you "expected" this, but when I queried Fig. 2 in the Berkeley paper which indicates that this already occurs at zero voltage, you said that it is correct! Stop playing games.

Um. No, "normal tunneling" requires higher voltage. Look at the curve. Where do you see evidence of "normal tunneling" "at zero voltage"?

From the Berkeley paper that you pushed under my nose. In Fig. 2 it is written that "The vertical line shown is due to the tunneling of cooper pairs, while the sloped lines are due to the quantum tunneling of single electrons". And guess what is the lowest voltage at which the sloped lines start? At V=0.

At this point I must first retire and try to figure out why people can be so dishonest!

 

[sol invictus]

I cannot remember all of the text books I have scanned in libraries; but I have already mentioned Fig. 44-15 in Serway; although it is not a text book on superconduction.

And which contradicted you, yes.

Since you asked, I quickly looked on my shelf which is not the best library; but can quote:

Andrei Mourachkine: book published by Cambridge International Science Publishing (see page 48).

I just spent 15 minutes acquiring that book and reading that page. There is no mention of current, no mention of voltage, no mention of J junctions. It's about the crystal structure of cuprates and its effect on Tc.

What a waste of time. Enough of this nonsense.

 

[Ziggurat]

At this point I must first retire and try to figure out why people can be so dishonest!

Go see your neurologist. Get yourself checked out. That might help.

 

[ben m]

So you did lie when you said it makes no difference!!!!!

Read it again. And again. And again. You've got a hair trigger for "lies", and firing every time someone says something you didn't expect. Your misreading of my words does not mean that I'm lying.

So once again you force me into boring pedantry. I have said the following two things:

"You have to look at the whole circuit". It's true, you do. The Scalapino circuit behaves differently than a plain single SIS junction. If you pretend that it's a single SIS junction, you will misunderstand the data.

"A capacitor doesn't change the voltage or current in a DC circuit". This is true. That is looking at the whole circuit---look at a circuit with a capacitor in parallel, keep track of the whole thing (as we do with the Scalapino circuit) and we find that the capacitor doesn't change the current or voltage in the DC circuit. As it turns out, then, in this specific case, ignoring the capacitor does NOT make a difference.

Which one of those is a lie? Quote me where I said something wrong.

 

[ben m]

First Goebbels, now Saddam Hussein. Your paranoia is indeed very impressive.

I drew "apartheid-era thug" at one point.

 

[johanfprins]

Comments on post #1149 by Ziggurat

I don't care what cancels the field. The fact remains, the field is canceled. And you HAVE claimed the field is canceled, many times. So regardless of what causes the cancellation of the field, the field is still zero, and so it exerts no force on your dipoles.

So God Ziggurat knows and will not allow Him/Her to be confused by experimental facts. The field is cancelled at the positions of the charge-carriers by an opposing polarization force and this force does not disappear when a current flows with zero voltage. This is an experimental fact; no matter what you want to believe.

Of course I agree with that. That in fact was one of our points of contention very early in the thread. I stated repeatedly that you could have an electric field inside a superconductor, and you could accelerate charges in a superconductor.

If you can accelerate charges the voltage will never drop to zero.

Zero resistance and nonzero voltage requires that the current changes over time,

The current within a superconductor does not change owing to acceleration but owing to a change in polarization of the charge-carriers.

Everything I've said has been consistent with that.

But it is not what really happens in a superconductor since if acceleration of the charge-carriers is possible the voltage cannot become zero.

You, however, have not been consistent at all.

Your "consistency" is not borne out by experimental results; and therefore you are consistently wrong. What you want to believe is my "inconsistency" is borne out by experimental results as being consistent. In physics experimental results are always the final word. Obviously you believe that it is not so!

No, johan. Work always needs to be done to accelerate any particle from rest, but if a charge carrier moves into a superconductor, guess what? It's already moving.

At what speed? So you claim that the speed of charge-carriers within a superconductor is totally determined outside the superconductor and not by the superconductor itself? But in the next breath you claim that this speed is determined by acceleration within the superconductor: You really are "consistent" are you not?

The work can be done external to the superconductor.

I thought you just now claimed that it is done by acceleration within the superconductor.

The relevant difference is that the contact point is not itself a barrier.

Oh but there is always a barrier between any two materials; even different metals: Have you never heard of a thermocouple? To lower the barrier you have to form a dipole-layer over the interface

But the contact point between a cathode and the vacuum gap IS a barrier.

Which you can eliminate by heating the cathode.

That makes a vacuum diode intrinsically different than a superconductor.

According to your model they are the same except that for a superconductor the field between the contacts evaporate as if by magic. This is not possible within any material, also the vacuum (which BTW is also an electronic material), when the charge-carriers can be accelerated as you claim happens within a superconductor.

 

[johanfprins]

Comments on post #1150 by sol invictus

I refuse to keep on repeating the obvious just because sol invictus cannot understand it.

 

[Ziggurat]

So God Ziggurat knows and will not allow Him/Her to be confused by experimental facts. The field is cancelled at the positions of the charge-carriers by an opposing polarization force and this force does not disappear when a current flows with zero voltage. This is an experimental fact; no matter what you want to believe.

Wow. You're really losing it. You claim that there is no voltage, which means that there's no electric field. And yet, a force somehow still exists due to this field, even though the field is zero. Quite the trick, getting a non-existent field to apply a force.

Yeah, sorry, that's not an experimental fact. That's utter nonsense. And it's sadly par for the course with you.

 

[johanfprins]

Comments on post #1152 by sol invictus

I just spent 15 minutes acquiring that book and reading that page. There is no mention of current, no mention of voltage, no mention of J junctions. It's about the crystal structure of cuprates and its effect on Tc.

I am sitting here with the book open in front of me and pages 45 to 55, which includes page 48, are totally about Josephson Effects. Do you know how to find a page in a book?

 

[johanfprins]

Comments on post #1153 by Ziggurat

Go see your neurologist. Get yourself checked out. That might help.

Thanks I will try it. We all can do with a bit of help unless, of course, you are God Ziggurat!