最近、韓国が元気だ。
モノマネから脱却して
クリエイテイブな研究者がぽちぽちと
出てきたのか。
室温超伝導ができたという。
私も四十年以上前に室温超伝導ができたと思ったが
再現しなかった。
一部転載：
Breaking Superconductor News
I wrote recently about the turmoil in the field of higher-temperature superconductors, but little did I know what was coming. Yesterday two preprints appeared on the rXiv site, the first bearing the attention-getting title “The First Room-Temperature Ambient-Pressure Superconductor”, and the second going into more detail about its behavior. As you’d imagine, this made something of a splash during the day on Tuesday!
Let’s look at what’s being claimed, and how strong the evidence seems to be. The authors describe a lead-based copper-doped material, LK-99, which is made by first preparing a well-characterized mineral (lanarkite, Pb2(SO4)O) from lead oxide and lead sulfate. Separately, copper phosphide (Cu3P), another well-characterized compound, is also freshly prepared from elemental copper and phosphorus. These two substances are ground together in a 1:1 ratio and the mixture is sealed in a vacuum-evacuated quartz tube and heated to 925C, forming LK-99, which is Pb10-xCux(PO4)6O, a dark polycrystalline material. The structure is very similar to lead apatite, a well-characterized phosphate mineral, but its crystallographic unit cell is slightly smaller due to the substitution of particular lead atoms in its lattice by copper ones.
And it’s this effect on the compound’s structure, the authors believe, that leads to its extraordinary superconducting behavior. Honestly, “extraordinary” doesn’t get it across. We’ve been getting excited over the years about superconducting materials that don’t even quite have to be cooled with liquid nitrogen, and this stuff is claimed to superconduct all the way up to room temperature and indeed up past the boiling point of water. Its critical temperature is said to be 127C (!) The phrase “boiling-water superconductor” is not one that I had ever used until yesterday, trust me on that.
The authors believe that the modified/strained structure of their material creates a large number of “quantum wells” between particular lead atoms and the adjacent oxygens of the phosphate groups bound to them, in effect making a two-dimensional “electron gas”. They propose that electron tunneling between these quantum wells, which are between 3.7 and 6.5 Ångstroms apart, is the superconducting mechanism. I am not enough of a solid-state physicist to judge this proposal, but the authors are making a detailed mechanistic claim that is subject to experimental proof, which is very good to see, and and they adduce a good deal of data to back it up (x-ray diffraction, EPR, and more). And they demonstrate the behaviors that a superconductor should have, such as the Meissner effect (expulsion of a magnetic field), sudden resistivity changes at a critical temperature (bizarrely high though that is in this case), current-voltage (I-V) plots at different temperatures and under different magnetic field strengths, etc. If these data reproduce, the superconductivity of this material seems beyond doubt. (Added note: others have pointed out that they'd like to see heat capacity measurements as well, which the paper doesn't show).
Another welcome feature is that their procedure for preparing LK-99 seems quite straightforward. You can bet that furnaces in solid-state materials labs around the world have been cooking yesterday and today to try to reproduce its synthesis and the properties, and we should be hearing about the results of these experiments very soon. The first samples should be coming out of the quartz vessels. . .sometime tomorrow, perhaps? Depends on what was available around the lab! Now, as the world knows, all such claims to date have fallen apart on closer inspection - indeed, the superconductivity research group at Rochester that I wrote about earlier this month is now about to haveanother paper retracted on suspicions of data fabrication. But those reports were on materials that take very specialized equipment to make and evaluate - this new report looks like it’s either going to fall apart very quickly or be quickly vindicated (as were the 1987 superconductor discoveries). I absolutely cannot wait to find out.
I really, really, hope it’s as claimed - that should go without saying. And I’m going to be in a rather jumpy mood until we hear one way or another! That’s because this truly would be a world-changing discovery (as well as an obvious instant Nobel prize). Whether LK-99 itself becomes a big industrial material is open to question - one of the things you get from the characterization data is that LK-99 is not able to carry much current in its superconducting state at these high temperatures, and that’s a key property for many applications. That might not be surprising, either, because other superconductors generally carry less current density the higher the temperature gets (i.e., the closer to the critical temperature). But it has to be noted (see my earlier post linked above) that this is indeed a polycrystalline material as synthesized, and that junctions between the different crystal domains can affect this profoundly. We also don't have a feeling for how such a quantum-well superconductor behaves in general, if that's how it works. If this is real, vast amounts of work will go into seeing if that current density can be increased by more careful synthesis and fabrication.
But as usual, it's a gigantic step to just show that such things can exist. That’s what will shake everyone up well before any applications come along, and if this reproduces, labs around the world will frantically start looking for quantum-well superconducting materials of their own. Who knows what could come out of that? Robust high-current-density room-temperature superconductors are right out of science fiction (SF readers will recall that one such material was a big plot point in Larry Niven’s Ringworld). Electrical generation and transmission, antennas, power storage, magnet applications (including things like fusion power plants), electric motors and basically everything that runs on electricity would be affected. We could stop throwing away so much generated power on heating up the wires that deliver it, for starters.
LK-99 isn’t that material, or at least not yet. It may not be anything - we’ll know soon. But it could also signal a transition point in human history. Place your bets, folks, place your bets.