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Physicists May Be One Step Closer To Explaining High-Temp Superconductivity
sciencehabit writes For years some physicists have been hoping to crack the mystery of high-temperature superconductivity—the ability of some complex materials to carry electricity without resistance at temperatures high above absolute zero—by simulating crystals with patterns of laser light and individual atoms. Now, a team has taken—almost—the next-to-last step in such 'optical lattice' simulation by reproducing the pattern of magnetism seen in high-temperature superconductors from which the resistance-free flow of electricity emerges.
superconductors, not semiconductors, genius.
Superconductive materials have 0 resistance which means there is no energy lost to heat.
As for how easy these temperatures are to hold, see your local hospital and ask them how easy it is for them to maintain their MRI machine's superconductive magnets.
What understanding the underlying properties of super conductive materials allows is for us to perhaps engineer some meta-materials that hold such properties at room temperature.
You will always have heat buildup to deal with in any system that does something useful.
Superconducting magnets are useful, even if they're not doing work.
perhaps engineer some meta-materials that hold such properties at room temperature.
Doesn't even have to be room temperature. Being able to make a MRI machine using liquid nitrogen instead of helium would be a huge win.
True, but last time I read up on this their superconductivity broke down when they carried high currents. They're superconductive enough to be useful, for example making very powerful magnets for NMR machines, but not capable of carrying unlimited current.
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138K = -211F
The key threshold is 77K. Above that, and you can cool with liquid nitrogen. A liter of liquid N2 costs less than a liter of milk. A liter of liquid helium costs about a hundred times as much.
Even though there are higher temperature superconductors, and even if room temperature superconductors are discovered, MRI machines will probably continue to use liquid helium. Superconductivity not only stops when a critical temperature is exceeded, but also when critical magnetic fields are exceeded, and the magnetic field limit increases with lower temperature. So a lot of LN2 superconductors are still used with liquid helium, because you then can have more current and hence more magnetic field for using less superconducting wiring. Higher fields for MRI machines mean more options like higher SNR, better resolution, or quicker measurements. I would expect ambient magnetic field MRI equipment (using Earth's magnetic field with sensitive detectors like SQUIDs) would be the direction low cost, non-cryogenic MRI machines to take in the future if room temperature superconductors were found.
I think you may have misread a bit - cheap liquid nitrogen boils at 77K, making it ideal for pre-cooling/outer jacket cooling. Most superconductors on the other hand only work their magic at substantially colder temperatures, which require much more expensive liquid helium cooling (liquid He is 100s of times more expensive, as I recall).
High temperature superconductors are those which operate at temperatures above 30K, with the highest I could find reference to operating at 138K - a range which could easily operate with only liquid nitrogen cooling. Such materials start to open the door to realistic superconducting power distribution, etc, but only in a few very specific cases - it's still radically more expensive than normal conductive wire after all. If we manage another 100K or so jump in superconducting temperature we'd start to get into the range of more traditional cooling systems, even if it's still well below freezing (273.15K). At that point the costs for cooling drop enough that superconductors would start to be attractive for a much wider range of applications.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
The highest temperature superconductor (HgBa2Ca2Cu3Ox(HBCCO) acts at temperatures at or below -140C (-220F). That is still darn cold. Dry Ice sublimates at -78C. What I would consider practical would be around -5C (which means we have 140C to go). Some would want it to be 25C or higher, but you could run a 'national grid' at -5C where "power pumped in" = "power pumped out" without loss. And it would save I2R losses by boatload. Clearly when you look at the number of chemicals and the structure of what they are creating to get to superconductivity, shotgunning it may not be as good as a sound theory of how things work. Every advance gets us closer to a crapload of money and the ability to use electric cars using a power grid similar to what we have now.
The System is continuous. There are no scale, quantum, or relativistic effects.
Utter rubbish, laddie, quite like that image you linked to. Modern thermodynamics has no such limitations. Go look up negative temperature (hint: you might have heard of such things as lasers) for a fun, discrete, quantum thermodynamic system. Heck, Planck's black body radiation was a nice, discrete, quantum thermodynamic system. Ye might want to resort to a teacher that's been around at some point during the last century or so, next time you argue thermodynamics. Such a one might point you towards such things as Bose-Einstein or Fermi-Dirac statistics and their thermodynamic interpretation. As for relativistic effects, look up thermodynamic models white dwarves, to begin with.
The laws of thermodynamics are relevant only within a narrow range of physical phenomena, which we have gotten out of.
Conservation of energy (first law) is quite relevant at pretty much any scale that was tested so far. Entropy increase and irreversible processes (second law), same thing (although there are interesting points about it w.r.t. black holes). Third law, entropy goes to a finite (sometimes zero, sometimes not) value as temperature approaches 0K was tested with quantum systems, as those are the only ones relevant at that temperature scale (thermodynamic fluctuations drop below quantum ones).
Now, the GP has a partial point, the superconducting part of the circuit does no 'useful' work, that does not mean the rest of the circuit doesn't either. Transport is important, as anyone who ever saw a superconducting magnet knows well (those things tend to be hard to transport, too). Thermodynamics gives one an upper limit of efficiency, superconducting wires simply move the efficiency closer to the theoretical limit. Overall entropy of the system increases, even if we manage to constrain it inside the superconductor (well, on the surface, mostly).
Tcs of Superconductors have been far above liquid Nitrogen for 30 years
Yeah, in brittle ceramic form. Something other than cuprates would be nice, preferably something useful ... and not too reliant on rare earths. That's the whole point of the exercise, bloody CuO plane is weird and it's been hard to study, nevermind to make for industrial applications. So they're trying to simulate it, which is quite cool imo. Personally, I'm still betting on AFM insulator effects over Mott insulator ones, but it remains to be seen.
Must be funnier in German
Wherever You Go, There You Are
Um, yeah, that's what they do in MRIs. Only have to energize it and keep it cool. They get really ticked if they have to turn it off - very time consuming and expensive to turn it back on again.
A "low temp" superconductor relies on liquid helium to keep it cool (approx 4K). A 'high temp" superconductor relies on liquid nitrogen to keep it cool (77K).
Liquid nitrogen is stupidly cheap - tons of places use liquid nitrogen for a lot of non-superconducting purposes including packaged food preparation, cooling, experimentation (a lot of "cryo" experiments use liquid nitrogen, including the ever popular frozen rose, frozen banana and other science demonstrations).
In fact, to get rid of a small dewar of liquid nitrogen, it's usually just dumped on the table after the demo is done creating a nice effect. A more controlled evaporation is simply leaving the lid off and letting it boil off naturally.
No one keeps stuff cool by liquifying nitrogen onsite. Instead, they just have Air Liquide and similar companies come by every week or so and top off the cryo tank. The cryo tank provides the supply of liquid nitrogen that's needed for the equipment (MRI machines use it in superconducting magnets). Most labs have it available freely as well.
Liquid helium is much more expensive. Liquid nitrogen is so cheap that having it transported and even any wastage is considered "meh". Hell, schools probably buy way more than they need simply because to make it worthwhile you end up with a huge dewar of it.