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)