Author Topic: Room temperature superconducters  (Read 1576 times)

Offline Grawk1

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Room temperature superconducters
« on: January 24, 2014, 05:46:00 PM »
So I saw this linked on Reddit and I wondered what you had to say about it:

http://nextbigfuture.com/2014/01/oak-ridge-national-lab-provides-partial.html

I admit, I don't have a clue what half of that means, but it seems like they are claiming that they may have developed a room temperature superconductor. I'm looked for confirmation and context elsewhere and found nothing. This seems pretty sketchy (I'm guessing that history's greatest scientific breakthroughs don't usually get covered exclusively on blogspots drowning in obnoxious ads) but could you tell me what this means and how plausible it is that we'll have room-temp superconductors in the near future?

Offline scikopas

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Re: Room temperature superconducters
« Reply #1 on: January 25, 2014, 12:44:29 PM »
Confirming something like that is basically what I worked on for the last year, and frankly I'm glad the project is over...

There are a number of claims of partial superconductivity at high temperature.  I worked with a group that thought they had found 20% superconductivity very near room temperature. The effect was confirmed by three labs (including JPL) but nobody could say what it was for sure.  These anomalies are usually sample-specific, and can only very rarely be reproduced (the growth processes are inconsistent).  I'm embarrassed to admit that I even had myself convinced I had something at one point.  They get spread around because these people need money immediately, so they advertise a partial, unconfirmed result to investors, so get more funding to continue the experiments.   There are hundreds of patents filed in a rush after they think they found something, but no good scientific papers because nobody can really reproduce or explain why/what is happening.

I don't think I can go into any more detail about my findings right now, because we're getting ready to submit a paper on it (don't worry, it isn't that exciting, mostly about how to grow and how to actually measure these properly)...

The biggest problem with room temperature superconductivity is that nobody really understands the mechanism for high temperature superconductivity, so we can't say whether it really is or isn't reasonable for it to exist at room temperature.  Metals and low-temperature superconductors (<~15K) are covered by BCS Theory (Bardeen, Cooper, Schreiffer--the three scientists who worked on it) but the traditional cooper pair model does not really fit with high temperature superconductors like YBCO (77K) and BSCCO (110K). 

Theres no reason why its impossible, but according to M.R. Beasley, we should be looking in the region of low-anisotropy materials (directionally independent), with very high pair binding energies (how "strong" the superconductivity is).  Unfortunately this will mean very small cooper pairs, that are a lot harder to deal with because it also means we have a very small coherence length, so we would need an extremely high carrier density right on the surface of the material.    The best resource is probably what Beasley published in MRS Bulliten 36 (2011) (http://dx.doi.org/10.1557/mrs.2011.159) or his presentation based on the paper http://www.physics.umd.edu/courses/Phys798I/anlage/AnlageFall12/Beasley_Search_For_Practical_New_Superconductors_ASC2012.pdf


PhD student in Materials Science at Arizona State University currently working on high-temperature superconductors and quantum computers or something.
my (materials) science podcast: LASER (Let's Agree Science and Engineering are Rad!) twitter @scikopas

Offline Dodo Bird

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Re: Room temperature superconducters
« Reply #2 on: February 03, 2014, 11:04:14 PM »
Hello aliencam!

I always enjoy hearing more about this sort of stuff.  Have you done any reading personally on the theoretically predicted material Stanene? 

I would enjoy hearing more about the possible room temperature superconductivity of this type of topological insulator and more about topological insulators in general.

Thanks!

Offline scikopas

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Re: Room temperature superconducters
« Reply #3 on: February 04, 2014, 06:05:45 PM »
Topological superconductors and insulators are pretty tricky Stanene is a 2-dimensional layer of Tin (like the "graphene equivalent" but with Sn instead of C).  Some materials in 3-D are topological insulators, but when grown in 2-D schemes (the atom-thick layer again) just the very edge of the material is a topological superconductor.  Some of these are graphene, BiTe, HgSn, SbTe3, and probably lots of others.  Basically what happens is that almost all of the material is insulating, but right on the edge or corner, it becomes superconducting due to some effect that I don't understand well enough to explain.  This is only on the very very edge, so even 1 atom into the material the effect is gone.

Some problems with making actual devices out of this would be that to be useful, you need to have a really high current density in that very tiny area that is superconducting, and figuring out what kinds of geometries would fit together and keep the superconductivity across a device...    SC Zhang at Stanford does lots of research into this, and you can read some of his papers on the arXiv.   

Here's their current theory about the topological superconductors: http://arxiv.org/abs/1206.1407  (I don't understand much of it right now)  and here is the abstract for the paper that made lots of people excited about the stanene recently: http://prl.aps.org/abstract/PRL/v111/i13/e136804 .   They were able to calculate from first principles that it should behave like a superconductor within the quantum hall effect (for a while there was some debate) which means that you are able to see differences in the density of states as you scan a magnetic field which means... (this could get messy if i go too much further) that there are differing numbers of available energy levels for electrons to exist in (remember the Pauli exclusion principle that says two electrons cannot be in the same "state" at the same time, well the number of states that exist in a material at a certain time can change!).  Its really interesting science, but pretty heavy into materials physics, and this particular topic is a little complicated to explain without diagrams and plots and math...   I think its probably best to wait for an experimental result before going much further, because theres a lot that nobody is sure of yet.


-cameron
PhD student in Materials Science at Arizona State University currently working on high-temperature superconductors and quantum computers or something.
my (materials) science podcast: LASER (Let's Agree Science and Engineering are Rad!) twitter @scikopas

Offline Dodo Bird

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Re: Room temperature superconducters
« Reply #4 on: February 04, 2014, 10:18:56 PM »
Thank you very much for going into such great detail and for linking me to some excellent science.  I remember having the Pauli exclusion principle expertly explained to me on an episode of Titanium Physicists (I'm sorry, I tried to find which one but it currently eludes me) so this does make sense to me.

I will do some more reading and hope that someone on the Brachio network puts together a show to explain these materials in more detail.  (hopefully using bees in the analogy :))


Thanks again Cameron!