Talk:Superconductivity

The superconducting state breaks no symmetry

Clearly, the simple s-wave superconducting state does not break the local gauge invariance (it is still there in the superconducting phase) or any other symmetry for that matter. Therefore, I find the sentence "The existence of these "universal" properties is rooted in the nature of the broken symmetry of the superconductor and the emergence of off-diagonal long range order." a bit confusing. Maybe it can be modified to "The existence of these "universal" properties is rooted in the formation of a condensate of charged particles and the emergence of off-diagonal long range order"?

Rutger's Formula

Hello,

My draft for a stub on Rutger's Formula was declined. According to a frequent editor, this was mostly due to "lack of context". I think it might work instead as a section of this article.

Is this a possibility?

Miguelmurca (talk) 10:21, 14 October 2019 (UTC)

Google seems to find more refs (which seems to be the main reason the draft was declined) - but the content seems to be mostly about the derivation of the formula - which seems too detailed for this article. Can I suggest adding more refs to the draft, extending its introduction, and putting a very brief mention to Rutger's formula where/if this article talks about a step change in specific heat. - Rod57 (talk) 18:39, 4 January 2020 (UTC)

@Miguelmurca: I would suggest that the article needs some english language verbiage; notably, what does it mean? "discontinuity in the specific heat". I've had undergrad physics, I think I understand it, but this is wikipedia, not a textbook. Explain in words what happens to specific heat at Tc (a graph would be useful), and why we care about it across that boundary. Also, some history. Who was Rutger, and why is the formula named for him? All of this, obviously, with citations. I will also mention that you are likely to run into some paranoia about naming, so make sure it's clear with secondary sources that the name is widely accepted. Regards, Tarl N. (discuss) 21:42, 4 January 2020 (UTC)

Addendum, it seems likely that the draft is misnamed - "Rutgers Formula" looks to not have an apostrophe. Which suggests it's named after the university, rather than a person. Tarl N. (discuss) 21:48, 4 January 2020 (UTC)

Proposed series for superconductivity (Sidebar or Footer open for discussion)

Hi all, I created Template:Superconductivity which mostly contains all the links in the see also section of this article arranged in categories. I am no longer fully convinced it is needed, but thought it was a great idea when I started. (There are a lot of a articles here that relate to superconductivity and you have to follow a lot of links sometimes to find specific information) I would like to know what others think. If you like the idea, feel free to edit Template:Superconductivity to help make it more useful. Thanks! Footlessmouse (talk) 05:51, 15 August 2020 (UTC)

Hi Footlessmouse. My question is: where would you use it, where would you put it (in those articles), and how different is this from "See also". Sometimes, these templates become too big (you're already there), lose focus, and don't look very nice in articles (especially when people put them in the lead), so I have mixed feelings. But that's just me... Ponor (talk) 23:19, 15 August 2020 (UTC)

Hi Ponor, thanks for the reply. I agree that it already has too much in it. It would be better as a footer, I believe. The primary advantages of using the template, in my opinion, is 1) to reduce the size of the see also sections across the articles to only mention those articles that are most relevant to the current article (links to articles which a significant portion of new users are likely to follow after reading the current article). 2) To allow the template to be standardized across all the articles, so that it is easier for new users to surf around the topic. 3) To categorize the articles that would otherwise be in the see also sections, so that it is easier to find a specific topic of interest. The main disadvantages are maintenance and brevity. Like I said, I'm not convinced either way, but wanted to see what others think. Footlessmouse (talk) 00:02, 17 August 2020 (UTC)

I checked few articles with similar templates. Quantum Mechanics article has an enormous one, with collapsible sections. I have to admit I don't think I ever used any of these. I wonder if "See also" sections are that important. It's the wikilinks that we like to follow, because they (should) put things in context, not just list them. Templates may be good for our bookkeeping, but articles are best linked by wikilinks... imho. Ponor (talk) 00:56, 17 August 2020 (UTC)

If by wikilinks you mean links in the text that link to a subject when it is mentioned, then agreed. I believe that is, by far, the most useful means of navigation. I still use templates, though, but not too often. It's usally for the 3rd reason above, when I am surfing through random phenomena, experiments, or people tangentially related to a given topic. It also doesn't seem like this is too big of a deal and not too many are interested in it. If anyone else likes the idea, please let me know, otherwise we'll just leave everything as is for now. Thanks! Footlessmouse (talk) 01:23, 17 August 2020 (UTC)

FYI: Found this recent discussion, some interesting arguments against using the sidebars (e.g. They're missing from mobile pages, yet no complaints) @Footlessmouse:

https://en.m.wikipedia.org/wiki/Wikipedia_talk:Manual_of_Style/Lead_section#Sidebars_(navboxes)_should_NOT_be_used Ponor (talk) 11:57, 19 August 2020 (UTC)

This is interesting and it does make several good points. I can agree that the sidebars should be kept out of the lede and a picture, if available, should be the first thing in the upper-right-corner of the page. I will keep this in mind in the future. Footlessmouse (talk) 21:39, 19 August 2020 (UTC)

Don't Cooperpairs need energy to form / Maybe someone can explain

About this part of the article, right at the start: "... below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source ..." Well first of all the first source is down.

Then: As I understand it, the band gap is a dynamic balance. So there are continuously forming Cooper pairs and breaking apart. Every time a Cooper pair forms, it takes around 1 meV. That ain't much, naturally, but it is something... so wouldn't that energy change its form, ie not be part of the equation anymore, so that an electric current through a loop of superconducting wire should not persist indefinitely, but continuously "lose" an insanely small amount of energy, until nothing is left, unless you could create a superconductor at 0 Kelvin, which is proven to be impossible to reach?

I feel like zero resistance would somewhat break the laws of nature as it is the case with zero Kelvin. Maybe someone can clarify. --Leo Navis (talk) 19:39, 29 March 2022 (UTC)

Alrighty, I talked to a friend of mine who is an electrical engineer and he explained it like "Yeah, there is energy lost, but you wouldn't call that resistance, since you don't have resistance in a classical, Ohm way". If that is correct then the statement here is not correct: "An electric current through a loop of superconducting wire can persist indefinitely with no power source" and should be fixed. The sources are also not what I would like to see for such a spectactular statement; I feel like the sentence should just be deleted. --Leo Navis (talk) 07:39, 1 May 2022 (UTC)

There is no magic here: The supercurrent flows in the ground state of the superconductor, so it cannot decay (it is the lowest energy state). Brienanni (talk) 10:12, 1 May 2022 (UTC)

At some point, it is quantum mechanics and you can't explain it any other way. As well as I know it, to lose supercurrent, it has to lose it all at once. The Cooper pairs are one quantum state, and scatter all or nothing. And the all is hard. Gah4 (talk) 13:59, 1 May 2022 (UTC)

It would be great if you could give me a reliable source for that. The sources that are given there are clearly not enough, they don't explain or show anything.

My reasoning, again: as I have read it, the Cooperpairs in a superconductor over 0 Kelvin are in a dynamic state and therefore form and break apart all the time. Every time that happens it takes ~ 1 meV. 1 meV is an incredibly small amount of energy, but it's still energy. And if there's energy needed to keep the process going, it would not go on forever, as stated in the article.

Please give a good, reliable source that is able to sufficiently explain why and how there is no energy lost at all, who has proven that in what work. Because you must admit, that is a very bold statement, and if it is not, as I suspect, sufficiently proven, that sentence has no place in an encyclopedia, as it is mere speculation. --Leo Navis (talk) 18:33, 4 May 2022 (UTC)

No energy is lost because it the superconductor is in the ground state, there is no lower energy state available. The Cooper pairs are not in a dynamic state, they do not break apart, that would cost energy which is not available in the ground state. In any case, that the supercurrent does not decay is an experimental fact. For example, this publication https://doi.org/10.1103/PhysRevLett.10.93 measures a decay time larger than one hundred thousand years. Brienanni (talk) 19:35, 4 May 2022 (UTC)

"More than 100.000 years" sure is impressive. It is not infinite. So... that's not what I asked for. If you have a "decay-time larger than one hundred thousand years", then that's not "indefinitely". See my point?

The article claims, as a fact, that an electric current in a superconductor > 0K can persist indefinitely with no power source. So please, do deliver a viable source that that is actually proven. Not over 100.000 years. Not over a Million years. Indefinitely. If you cannot, we should take that sentence out or edit it. That sentence is IMHO an absurd statement because it's impossible to prove and should therefore not be part of this article or this encyclopedia. --Leo Navis (talk) 20:00, 4 May 2022 (UTC)

There are many exponentials in quantum mechanics, and I believe this is one. That is, the lifetime is exponential in the number of Cooper pairs in the superconducting ring. There is an old saying that ties the experimental number to the term of a graduate student, since they are the ones that do experiments. It doesn't take a very large exponent to get a very long time. If you run into a brick wall, there is a (very small) chance that you come through the wall through quantum tunneling. It is exponential it the thickness of the wall. For something that happens much faster, consider alpha decay of U238. An alpha particle moves inside the nucleus at about 0.1c, and bounces off the nuclear boundary, until it tunnels out. How many times does it hit before it gets through? (The nucleus is a few fm across, and c is 3e23 fm/s.) The time might not be infinite, only 10**(10**23) microseconds. Gah4 (talk) 07:06, 7 May 2022 (UTC)

Very well. So can we now please take this out? "Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source." --Leo Navis (talk) 20:23, 11 May 2022 (UTC)

Added the citations below to the sentence in question:

• "An experiment always has a limited accuracy... Nevertheless experimentalists have pushed as far as they could to determine how small the resistivity of a superconductor is. For a superconductor... no dissipation occurs so the induced currents can persist indefinitely. This kind of experiment has been repeated, persistent currents have been observed for several years, and the decay time for the persistent current has been evaluated as ~10⁵ years. This comes quite close to an experimental proof of [zero resistance]." Roland Combescot (2022) Superconductivity: An Introduction, Cambridge Univ Press, p.1-2
• "Since R=0, there is no energy dissipation (I²R loss), a current set up in a closed loop of a superconductor persists forever without decay." Ajay Kumar Saxena (2009) High Temperature Superconductors, Springer Science, p. 215
• "It is, however, still possible to arrive at the reasonable conclusion ρ → 0 [no resistivity] by inference from real measurements. In such experiments the magnetic field associated with an induced current has been found to remain counstant over a time span as long as one year. [...] The resulting analysis of such an experiment leads to the conclusion that the lower bound on the decay constant τ for the current in the superconductor is of the order of 100000 years, implying that the total time for the current to die out completely would be millions of years." Kristian Fossheim, Asle Sudboe (2005) Superconductivity: Physics and Applications, John Wiley and Sons, p. 7

--Chetvorno^TALK 21:06, 11 May 2022 (UTC)

"This comes close to proof" and "implying that the total time for the current to die out ... would be millions of years" is not "indefinitely" and not "proof". Why are we not just writing it like it is writte in the sources? Why must we talk here like something that, from these sources clearly shown, is not proven at all, but instead not just talk of it how it's reasonable to talk about it? Why claim factuality when that isn't justified by the material? --Leo Navis (talk) 09:02, 14 May 2022 (UTC)

It can only last as long as someone keeps supplying coolant. I am not sure about differences in High-Tc materials compared to traditional metals. What do actual sources say? Gah4 (talk) 18:12, 14 May 2022 (UTC)

This one says indefinite, which is different from infinite. Gah4 (talk) 18:17, 14 May 2022 (UTC)

I take "Indefinitely" to mean "longer than any practical measurement timescale". That's not the same as "infinite". Infinity is too strong a word. Would it be preferable to describe the resistance as "unmeasurably small"? There are other forms of persistent motion. For example, the magnetic moment of a microscopic piece of iron metal will persist indefinitely. A rock will remain perched on a hill indefinitely. None of these timescales are truly infinite, but neither are they gradually decaying. I wish for the reader to understand that a superconductor is not simply a better conductor than copper. (this is my first edit in the comments for a long time, so I'm trusting the editor; notify me or edit my comment if I've left a mess) Spiel496 (talk) 00:00, 5 June 2022 (UTC)

Recently (not in WP) someone asked about gamma rays from hot objects. You can take the black body spectrum out to 2.3MeV, and, from my calculation, it is 1e-100. So not zero. As well as I know, superconductivity is not gradually decaying, like a single radioactive atom doesn't gradually decay. It either decays or it doesn't. Quantum mechanics is good at coming up with small but non-zero probabilities. What is the probability of you suddenly quantum tunneling to pluto? Not zero, but extremely small. As well as I know, superconductivity is exponential in the number of Cooper pairs. Gah4 (talk) 02:08, 5 June 2022 (UTC)