# Thermal superconductivity **URL:** \ **Category:** Factual Questions\ **Created:** [April 6, 2001, 2:33am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013 "2001-04-06T02:33:08Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![boyce](https://avatars.discourse-cdn.com/v4/letter/b/13edae/32.png) [@boyce](https://boards.straightdope.com/u/boyce)\ **Post date:** [April 6, 2001, 2:33am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/1 "2001-04-06T02:33:08Z")
I’m looking for an answer from someone in the know; I’ve done quite a bit of web searching and have yet to see an informative discussion of the topic. Are electrical superconductors also thermal superconductors? Are there any limits on the ability of real, physical thermal superconductors (if there are any such things) to transfer heat? If I have a length of thermal superconducting wire, which is initially above its critical temperature for superconductivity, and plunge one end into a bath of fluid that is below that critical temperature, what governs the heat transfer along the wire? Thanks in advance. -Boyce ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [April 6, 2001, 3:46am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/2 "2001-04-06T03:46:59Z")
The short answer is no. Heat is transferred by 3 main methods - conduction, convection, and radiation. A typical piece of superconducting wire on a block transfers heat via all three methods. Put it in air, and it can still transfer heat by convection and radiation. Put it in a vacuum, and it will still transfer heat via radiation. Put it in a theoretical perfectly reflecting chamber, in a perfect vacuum, and with the surroundings all at the same temperature, and you may end up with a thermal superconductor. But the two are not related at all, and one does not really influence the other. A very simple basic way to look at it is superconductivity is a feature of the relationships between the electrons and their shells, while thermal energy is a feature of the overall movement or vibration of the entire atoms themselves. I know, oversimplified, but it works for a quick explanation. If you stick one end of your wire in a cold source, heat is transferred out of the wire by conduction and convection between the wire’s surface and the fluid. The thermal energy of the motion and vibration of the atoms in the wire is transferred to the slower moving/vibrating cold fluid, thus heating it while the wire cools. Is there perhaps something else that you are asking when you ask “what governs” the heat transfer? ---
**Author:** ![mok](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mok](https://boards.straightdope.com/u/mok)\ **Post date:** [April 6, 2001, 5:06am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/3 "2001-04-06T05:06:12Z")
One quick example: Helium II (superfluid Helium) is a thermal superconductor - its thermal conductivity is about 3x10[sup]6[/sup] times greater than “normal” Helium. However, it is _not_ an electrical superconductor. Conversely, mercury is an electrical superconductor near absolute zero, but it is not a thermal superconductor. But the phenomena certainly _are_ related, in fact this is an area of intense study. Obvious parallels include: [ul] [li]Both are very-low-temperature phenomena, appearing only below some critical temperature[/li][li]Both exhibit anisotropy (different behaviors when measured along different directions)[/li][li]Both are associated with the behavior of electrons in various states of excitation[/li][li]Electrical superconductors do exhibit changes in thermal conductivity as they approach their critical temperature[/li][li]Both phenomena have something to do with the interaction between electrons and phonons (vibrations, essentially)[/li][/ul] -m ---
**Author:** ![boyce](https://avatars.discourse-cdn.com/v4/letter/b/13edae/32.png) [@boyce](https://boards.straightdope.com/u/boyce)\ **Post date:** [April 6, 2001, 5:09am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/4 "2001-04-06T05:09:59Z")
Anthracite- Point well taken about the radiation and convection boundary condition issues. I was thinking however, that in addition to temperature manifesting itself via vibrational energy in the lattice, it also is carried by free electrons in the material. Any temperature gradient, it follows, should result in a gradient in electrical potential. I’m pretty sure this is how a thermocouple works. It seems like an electrical superconductor shouldn’t be able to withstand an induced voltage; it should respond with a large restorative current. Wouldn’t this result in an always isothermal superconducting body? To take your augmentation of my original example, if you have various wires with different thermal conductivities, the steady-state temperature gradient in the wire is a strong function of the wire’s thermal conductivity. As the thermal conductivity increases, the gradient decreases (all other conditions (radiation, convection) being the same). In the limit of infinite thermal conductivity, the wire is isothermal, even though heat is constantly being exchanged between the wire and the environment and the wire and the cold bath. I’ll have to think a bit about m’s point about Hg… -boyce ---
**Author:** ![boyce](https://avatars.discourse-cdn.com/v4/letter/b/13edae/32.png) [@boyce](https://boards.straightdope.com/u/boyce)\ **Post date:** [April 6, 2001, 5:13am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/5 "2001-04-06T05:13:29Z")
m- Does this mean that at least for some superconductors the electrons and phonons are isolated? They don’t communicate at all? Does this apply to the high temperature superconducting ceramics? -boyce ---
**Author:** ![boyce](https://avatars.discourse-cdn.com/v4/letter/b/13edae/32.png) [@boyce](https://boards.straightdope.com/u/boyce)\ **Post date:** [April 6, 2001, 6:20pm UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/6 "2001-04-06T18:20:35Z")
In re-reading the above, I think “free electrons” should probably be “conduction band electrons”. I hope that clarifies a little… Can anyone clarify on the coupling between conduction band electrons and phonons in a superconductor? ---
**Author:** ![boyce](https://avatars.discourse-cdn.com/v4/letter/b/13edae/32.png) [@boyce](https://boards.straightdope.com/u/boyce)\ **Post date:** [April 6, 2001, 6:22pm UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/7 "2001-04-06T18:22:23Z")
In re-reading the above, I think “free electrons” should probably be “conduction band electrons”. At least I think that’s more correct… Can anyone clarify on the coupling between conduction band electrons and phonons in a superconductor? -boyce ---
**Author:** ![boyce](https://avatars.discourse-cdn.com/v4/letter/b/13edae/32.png) [@boyce](https://boards.straightdope.com/u/boyce)\ **Post date:** [April 7, 2001, 6:28am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/8 "2001-04-07T06:28:52Z")
Okay, in talking around about this with some other folks, the distinction between Type 1 and Type 2 superconductors came up. Does this govern the communication between electrons and phonons? No solid state physicists here? -boyce ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [April 7, 2001, 11:55am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/9 "2001-04-07T11:55:53Z")
> [@](#): > > \*Originally posted by m \* > \*\*One quick example: Helium II (superfluid Helium) is a thermal superconductor - its thermal conductivity is about 3x10[sup]6[/sup] times greater than “normal” Helium. However, it is _not_ an electrical superconductor. \*\* I’m a little confused as to how you are defining thermal superconductivity. You are only considering conduction then? And would not a thermal conductive superconductor require an infinite conductivity? What I am trying to say is - I don’t know if the term thermal superconductor is really analagous at all to electrical superconductivity. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [April 7, 2001, 12:09pm UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/10 "2001-04-07T12:09:15Z")
> [@](#): > > \*Originally posted by boyce \* > **I was thinking however, that in addition to temperature manifesting itself via vibrational energy in the lattice, it also is carried by free electrons in the material.** Yes, in a conductor the translational motion of the free electrons contributes as well. In a nonconductor it is entirely lattice vibrations. > [@](#): > > **Any temperature gradient, it follows, should result in a gradient in electrical potential. I’m pretty sure this is how a thermocouple works. It seems like an electrical superconductor shouldn’t be able to withstand an induced voltage; it should respond with a large restorative current. Wouldn’t this result in an always isothermal superconducting body?** Ah, I see now. Well, from what I know the thermal conductivity is an additive effect - where the total conductivity is equal to the lattice wave conductivity plus the free electron conductivity. Or k = k[sub]l[/sub]+k[sub]e[/sub]. Is what you are asking this - does k[sub]e[/sub] go to infininty as electrical superconductivity occurs, thus making k approach infinity? ---
**Author:** ![boyce](https://avatars.discourse-cdn.com/v4/letter/b/13edae/32.png) [@boyce](https://boards.straightdope.com/u/boyce)\ **Post date:** [April 7, 2001, 9:00pm UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/11 "2001-04-07T21:00:05Z")
You got it, Anthracite, that’s my question exactly. In the question of thermal superconductivity, temperature plays the same role as voltage does in an electrical superconductor. The electrical superconductor doesn’t really care what voltage it’s at, but it can’t support any kind of internal potential difference. Similarly, a thermal superconductor has to be isothermal; any temperature difference is very quickly restored by an arbitrarily large heat flux. k -\> infinity. Thanks for thinking about the question, anyhow… -boyce ---
**Author:** ![voguevixen](https://avatars.discourse-cdn.com/v4/letter/v/b5ac83/32.png) [@voguevixen](https://boards.straightdope.com/u/voguevixen)\ **Post date:** [April 9, 2001, 8:58pm UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/12 "2001-04-09T20:58:46Z")
This topic is right up my husband’s alley, so I linked him to it thinking he’d want to contribute. (His thesis was on this stuff…and by thesis I mean a bound paper about the size of a phone book.) Here’s the response he sent me. Bear in mind that I have no idea what any of you are talking about, so I don’t know if this helps or not. > [@](#): > > To my knowledge there is no such thing as a “thermal > superconductor”. Here’s my two cents. > The definition of a thermal superconductor that this thread is using seems to be “a material having no thermal losses for a given heat flow or equivalently as one which could support heat flow without an end-to-end temperature difference”. This would be analogous to lossless current flow observed in an electrical superconductor. But the analogy is not complete. > An electrical superconductor must satisfy two conditions; 1)zero electrical resistance and 2)zero magnetic field inside, regardless of the environmental history (i.e. it doesn’t matter what the conditions were when it was cooled through its transition temperature). It is the interplay between the electric and magnetic fields which govern electric current flow in a superconductor (see London). I don’t see anything to play the role of > the magnetic field in a “thermal superconductor”. > In general, the thermal conductivity of superconductors is smaller, not larger, at temperatures below transition. This effect is exploited in the design of thermal switches used to thermally couple and decouple things in low temperature experiments. I think this reduction of thermal conductivity at temps below transition is because when in the normal state, most of the heat energy is carried by conduction electrons. When the material is cooled below the transition temperature, > the conduction electrons no longer scatter off the lattice in a way that they can exchange energy, so the thermal conductivity decreases by a factor of 100 or so typically. Hope that helps…I can forward an email to him if you’d like. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 9, 2001, 9:31pm UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/13 "2001-04-09T21:31:19Z")
**voguevixen** , perhaps you could forward this? > [@](#): > > An electrical superconductor must satisfy two conditions; 1)zero electrical resistance and 2)zero magnetic field inside. Is condition 2 truly part of the definition, or merely a property all superconductors (that we know of) have? The reason I ask is that condition 2 doesn’t seem necessary for the applications of superconductors we normally hear of (i.e. conducting electricity with zero ohmic losses). ---
**Author:** ![voguevixen](https://avatars.discourse-cdn.com/v4/letter/v/b5ac83/32.png) [@voguevixen](https://boards.straightdope.com/u/voguevixen)\ **Post date:** [April 9, 2001, 9:53pm UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/14 "2001-04-09T21:53:25Z")
It’s on its way…I was hoping he’d just register and answer, lol. Oh well, he’s sorta busy building a space probe and all. Your tax dollars wouldn’t be well spent on SDMB addiction. ---
**Author:** ![voguevixen](https://avatars.discourse-cdn.com/v4/letter/v/b5ac83/32.png) [@voguevixen](https://boards.straightdope.com/u/voguevixen)\ **Post date:** [April 10, 2001, 1:15am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/15 "2001-04-10T01:15:50Z")
> [@](#): > > Condition 2) is a necessary condition for a superconductor. i.e. without it you don’t have a superconductor so you don’t have lossless current > flow. See Rose-Innes and Roderick or Tilley & Tilley. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 10, 2001, 3:44am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/16 "2001-04-10T03:44:41Z")
Now, I’m not going to argue with **voguefox** (rule of thumb: Never argue with a specialist in his field, unless you’ve got equal or greater qualifications in the same field), but perhaps I can clarify a tad. Isn’t it impossible to produce any electromagnetic fields in a perfect conductor? If you attempted to create such a field, the unimpeded electrons (or other charge carriers) would instantly react in such a way as to cancel out that field. Correct? ---
**Author:** ![voguevixen](https://avatars.discourse-cdn.com/v4/letter/v/b5ac83/32.png) [@voguevixen](https://boards.straightdope.com/u/voguevixen)\ **Post date:** [April 10, 2001, 10:06pm UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/17 "2001-04-10T22:06:39Z")
> [@](#): > > In the static case, the electric field is zero inside any conductor, perfect, super or otherwise. However the static magnetic field is quite a different story. You raise an interesting point with your assertion of a “perfect” conductor. What you claim is half true. Suppose you have a fictitious “perfect” conductor, that is, one which supports lossless current flow below some critical temperature but does not exhibit the Meissner effect (magnetic flux expulsion or perfect diamagnetism observed in superconductors). Such a conductor would, as all conductors do, obey Faraday’s law of induction. Due to the lossless current flow in this perfect conductor the magnetic field inside could not change. Lossless > circulating currents would be set up to oppose any change. Suppose this material was cooled in zero magnetic field and then an exterior field was applied. The field inside would remain zero, as it would for a superconductor. But now suppose the material was first placed in a field, > then cooled and then the field was removed. The perfect conductor would respond by generating its own field in order to prevent the field on the interior from changing that is, it would trap the field. In a superconductor, the field would be expelled from the interior as soon as it > was cooled through transition. There would be no trapped field. A superconductor does not allow any magnetic field in the interior of the sample. So you see, a superconductor is quite a bit more than a ‘perfect’ > conductor. It is a material that exhibits both perfect conductivity and perfect diamagnetism. (I asked him yesterday if he was looking this up or if it was all in his head; he claimed it was all in his head and part of his right arm – haha. A little physicist humor for you, there.) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 11, 2001, 1:36am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/18 "2001-04-11T01:36:54Z")
OK, the _change_ in B is zero in a hypothetical perfect conductor (available from the same catalog that sells the massless strings and frictionless tables). I should have realized that… I guess that some of my E&M hasn’t been sinking in properly. And of course he was joking about the right arm part. Everyone knows it’s actually the left arm. ---
**Author:** ![boyce](https://avatars.discourse-cdn.com/v4/letter/b/13edae/32.png) [@boyce](https://boards.straightdope.com/u/boyce)\ **Post date:** [April 11, 2001, 5:24am UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/19 "2001-04-11T05:24:53Z")
Oh cool, an actual expert! voguefoxen: Can you add to the above info a little discussion of the distinction between type 1 and type 2 superconductors, and what effect that distinction might have on thermal conductivity? Thanks in advance! ---
**Author:** ![voguevixen](https://avatars.discourse-cdn.com/v4/letter/v/b5ac83/32.png) [@voguevixen](https://boards.straightdope.com/u/voguevixen)\ **Post date:** [April 11, 2001, 5:47pm UTC](https://boards.straightdope.com/t/thermal-superconductivity/61013/20 "2001-04-11T17:47:35Z")
> [@](#): > > \*Originally posted by boyce \* > \*\* > Can you add to the above info a little discussion of the distinction between type 1 and type 2 superconductors, and what effect that distinction might have on thermal conductivity? > \*\* Mr.Vixen is behind on his gyroscope testing, so I’ll attempt to field this from his paper. Note that (Hc) and (Hc1) are actually H subscript C and H subscript C1, etc. > [@](#): > > Superconductors may be classified as either type I or type II depending on the details of how they respond to an external magnetic field. As the external magnetic field is increased around a type I superconductor, screening currents are generated on the surface which generate a nulling magnetic field in the interior of the material (Meissner effect). The material behaves as a perfect diamagnet until some critical value of external field is reached (Hc). In external fields about Hc, the material is the normal state. Type II superconductors exhibit the same perfect diamagnetism up to their “lower critical field” value (Hc1). As the external magnetic field is increased beyond Hc1, lines of flux are allowed to penetrate the material, driving some regions normal while the rest of the material remaions in the superconducting state. The material is now in the “mixed state”, where an array of normal “cores” exixts within the superconducting bulk of the material. The material can still pass current without loss (however, Jc is reduced), and it still has a diamagnetic response to the external magnetic field, although no longer a perfect one. Further increase of the external field will allow more and more lines of magnetic flux to penetrate the material, weakening the diamagnetic response and reducing Jc until the “Upper critical field” (Hc2) is reached, above which the material is in the normal state. T=temperature, H=external magnetic field, and J=current density, if I understand the charts and graphs correctly. Two of the books cited are _High Temperature Superconductivity - An Introduction_ by Burns (1992) and _Introduction to Superconductivity_ by Rose-Innes and Rhoderick, 1978, if you’re looking for some good sources.