Are room temperature superconductors either likely possible at all, or anytime soon (next 50 years, say). It seems that scientists are trying to find materials that have a higher critical temperature, but am I right in thinking that we don’t really know why superconductivity works the way it does, so it’s a little bit of trial and error with new materials?
We do know, in general, why superconductivity works, but it’s not like we can just punch a formula into a computer and it’ll tell us what’s superconductive and with what critical temperatures. So, yeah, there’s a lot of experimentation and trial and error, but it’s not blind: They already know what sorts of things to look for.
As to whether there is a room-temperature superconductor, and when we’ll find it if so, nobody really knows. There’s no fundamental reason anyone knows of why there can’t be, but nobody’s found one yet.
Ceramic superconductors are proof that superconductivity isn’t inherently reliant on near- absolute zero temperatures; if it can be done at 130K there’s no obvious reason why it couldn’t happen at 300K.
Can somebody give a brief Straight Dope description of the how and why of superconduction?
Google wouldn’t be half as much fun. I don’t need a very thorough answer, nor do I need it fast.
A superconductor is something that conducts electricity with zero resistance. They have very interesting properties. For example, because there is no resistance, if you put some superconducting wire in a loop and induce a current in it, the current will continue to flow forever without any outside energy source. (This is not a perpetual motion machine, since any attempt to get work out of the flowing current will use up its energy.)
The problem with superconductors right now is that the only things we know of that will superconduct have to be very very cold. Either near-absolute zero or a little bit above in the case of ceramic superconductors.
They are therefore not very practical for building, say, power transmission lines. You would need a great big fridge to keep the lines cold.
But if you could find a superconducting material that stayed superconductive at normal temperatures, and you could make wire out of it, then you could transmit electricity with zero resistance losses. Nifty.
Ok so far, but how and why does room temperature become viable?
What’s special about temps around 0K, and how can that be reproduced at room temp?
Incidentally, room temperature superconductivity was (well claimed to be) experimentally observed in 2012 in graphite powder treated with water. The evidence is quite thin for now, but you can read the original paper on the ArXiV here: http://arxiv.org/pdf/1209.1938.pdf and a blog entry that gives a layman’s explanation here
The need to refrigerate the known superconductors makes them impractical for most purposes. The magnets in a MRI are superconducting because bulky refrigeration is acceptable for that application.
The special thing about low temperatures is that when thermal energy is low enough quantum effects can emerge. The quest is to find or create a special material where quantum effects aren’t swamped by heat.
Ok, now we are moving along!
*What *quantum effects? Why are they not currently apparent at room temp, and why does anyone think they would be?
To turn that around, what sort of ‘electronic friction’ happens at room temp but not absolute zero?
The real answer requires a very deep understanding of quantum mechanics (which I don’t have). But the basic idea is that at low temperatures, electrons can pair up to form Cooper pairs. The interaction is very weak, and so at too high a temperature, the pairs don’t form. For reasons that are beyond me, the pairs (unlike isolated electrons) have a gap in their energy spectrum. A bare electron can bounce off an atom and lose a little bit of energy. After a lot of bounces, you can lose a lot of energy. But a Cooper pair can only lose a big chunk of energy due to the gap. Smaller energy losses simply aren’t possible, and so the Cooper pairs can circulate around with zero energy loss.
Hm. So possibly one could supercool a material, and it would retain Cooper pairs as it warmed up, similar in concept to making a magent with a magnetic field?
IOW, there’s no material that is ‘natively’ superconducting at room temps? The search isn’t for a substance but a process?
No, it’s a material they’re looking for. Trying to keep the Cooper pairs intact as you warmed the material would be like trying to keep ice solid as you warm it above the freezing point: Even if you can manage to do it, it’s unstable, and will collapse into its normal state for that temperature at the slightest provocation. Rather, what they’re looking for are materials that, for whatever reason, can form Cooper pairs at higher temperatures.
It should be noted that they’ve already made tremendous progress. All metals are superconducting at sufficiently-cold temperatures (in the neighborhood of single-digits Kelvin), and for a long time, it was thought that superconductivity was only possible at those temperatures. Nowadays, though, we have materials that can superconduct as high as (checks Wiki) 138 K. And oddly enough, these materials are mostly things that, unlike metals, are terrible conductors, above their critical temperature.
Seems I need to do some homework. My ignorance is fighting back a bit. 
But I’m going to point out that superconducting temperatures could easily be reached and maintained in space.
So perhaps that’s a reason to build a moonbase, or at least a permanent orbital colony. Superconducting supercomputers.
Might even be profitable to lease processing time to institutions back Earthside, like happened in the old mainframe days.
Space isn’t cold. What it is a near-perfect insulator. Space stations and spacecraft have to think about cooling just as much as they do heating, depending primarily on whether it’s in sunlight or in shadow. A superconductor on the moon during lunar night might require no extra cooling. During lunar day, it might melt. If you put it underground, you’ll probably be too hot to superconduct. Maybe you could put a satellite in orbit and spin it so that it has one face always away from the sun, permanently in shadow, but even then, heat will tend to spread through the satellite to the superconductor.
Here’s a cool video of a superconducting disk floating around a mobius strip of magnets with explanations of how it all works.
I looked this up. There are certain orbits near the earth that are permanently in shadow. The ‘background temperature’ of space is 3k. This means that only passive refrigeration would be needed to keep superconducting equipment on a spacecraft cold (by passive I mean heat fins, coolant and pumps, things that don’t involve a heat engine)
Of course, the $10,000/Kg that it costs to place things in LEO makes paying for liquid nitrogen or liquid helium look cheap.
I also recall reading that the current crop of superconductors cannot support high magnitudes of current density; once the current density exceeds a certain value, the magical properties disappear. Is there any truth to this? If so, does this limit their use in high power applications?
FWIW, liquid nitrogen boils around 77k, so 134k superconductors are an entirely different ball game in terms of usefulness than the older liquid helium ones.
Space is not cold, agreed. Objects in space are cold, however. The Moon is cold.
As long as the device isn’t laying out on the surface during bright semilunar, it will stay cold.
There’s no issue with radiating waste heat from a superconducting device, as there’s no waste heat to radiate.
(Agreed that orbital devices are somewhat problematic. But if a communications satellite can manage the heat, a computing one could as well, I assert.)
But back Earthside, I think even liquid nitrogen is too cold for practical use. You could replace liquid helium cooling in devices such as MRI machines, but I think it’s still too cold to open up new markets and new devices. No chance of home use, for example.
I know, I know, not just anybody can lead the Boston Philharmonic. But with a thin baton of graphene, maybe an everyday smuck can do it without having to be immensely chill… 