Slashdot Mirror
Scientists Create Supersolid From Helium
jabberjaw writes "Nature is reporting that Pennsylvania State University researchers Eun-Seong Kim and Moses Chan have created a 'supersolid' from helium-4. Although a crystalline solid, the supersolid can flow much like a liquid. This is due to the fact that the empty compartments in the crystal move coherently, thus waves can progress through the lattice. The supersolid state can be compared to the superfluid state. Perhaps a condensed matter physicist can dumb the article down for layfolk such as myself?"
Sure it could be. Here's the abstract from Eunsong Kim's talk about it two days ago at Penn State University, courtesy of our friend Google:
When liquid 4He is cooled below 2.176 K, it undergoes a phase transition--Bose-Einstein condensation--and becomes a superfluid with zero viscosity. Once in such a state, it can flow without dissipation even through pores of atomic dimensions. Although it is intuitive to associate superflow only with the liquid phase, it has been proposed theoretically that superflow can also occur in the solid phase of 4He. Owing to quantum mechanical fluctuations, delocalized vacancies and defects are expected to be present in crystalline solid 4He, even in the limit of zero temperature. These zero-point vacancies can in principle allow the appearance of superfluidity in the solid. However, in spite of many attempts, such a 'supersolid' phase has yet to be observed in bulk solid 4He. Here we report torsional oscillator measurements on solid helium confined in a porous medium, a configuration that is likely to be more heavily populated with vacancies than bulk helium. We find an abrupt drop in the rotational inertia of the confined solid below a certain critical temperature. The most likely interpretation of the inertia drop is entry into the supersolid phase. If confirmed, our results show that all three states of matter--gas, liquid and solid--can undergo Bose-Einstein condensation.
This is not the first new state of matter announced this week.
/. but keep forgetting password...
. ht ml
The New York Times reported a "color gass condensate" when gold ions were bombarded with relativistic deuterons. In this condition, nucleons and quarks blur into a jello of gluons.
There are MANY more states of matter than solid, liquid, and gas. There's plasma, 2-dimensional fluids, 1-dimensional crystals, ambiplasma of partcies and antiparticles, photon crystals, and lots of others.
This is the golden age of physics!
Professor Jonathan Vos Post
Woodbury University
have an accounton
BTW, check out my "Periodic Table of Mystery Writers" at
http://magicdragon.com/UltimateMystery/periodic
rollovers and click to 100+ pages...
That's a fallacy. The flow rate of ordinary plate glass is so slow that it would take billions of years before there would be a measurable change in thickness. Here are some articles on the subject.
Sapere aude!
No actually, this does have something to do with Bose-Einstein Condensation. Now, IANATheoretical Physicist, but as I understand it, at the quantum level these results may be a manifestation of b-e condenstation in the solid phase (to date, b-e condensation has only been observed in the liquid and gas phases). Now, the original poster was a little bit out to lunch with respect to his description of what a b-e condensate is, do I still highly reccomend reading the wikipedia article. There's still a lot of work to be done before we really figure out exactly what's going on in this experiment, but it looks to have some pretty cool implications at the moment.
If you have trouble thinking of moving holes or vacancies, think of one of those puzzles that is all jumbled and has one square missing. You have to rearrange the puzzle by moving peices into that vacancy, which makes the vacancy move around.
You obviously did not read any of the 3 articles I linked to.
Plate glass used to be made by dipping a tube into molten glass (1000 degrees Fahrenheit or so), gathering up a blob, blowing that blob into a bubble, poking a hole in the bubble, and spinning the tube so that the bubble's hole opens up. Done correctly it makes a flat circle of glass with the end of the tube in the center. This glass is relatively even in thickness but it is still thicker in the middle then at the sides.
They let the glass cool and then cut it into squares with one side closer to the middle. This side is thicker than the rest of the piece and was usually placed toward the bottom of the window because it was reasoned that the heaviest part and strongest part should be at the base. It was not until the Float Glass process was invented in 1959 that truly flat glass was available. Up until then there would almost always be some parts of plate glass that were thicker or wavy, giving rise to the flowing glass myth.
Sapere aude!
Heisenberg implies that they (still) move, but has nothing to do with the fact they move all together. This latter fact is because helium atoms can all fall into the "same" lowest-energy state, because they are bosons and so do not obey the Pauli exclusion principle.
Suppose you have a metal. This has positive nucleii, bound electrons which screen most of the nuclear charge, and conduction band electrons which can move thorughout the lattice, but also help to screen the nuclear charge. The whole thing is electrically neutral.
Suppose then you have some cloud of negative charge. This charge will repel the local electrons, and will attract the local nucleii. The nuclear lattice will bend a bit towards the center of the charge cloud, generating a local region of increased positive charge density that is screened out by the cloud of charge, and the other electrons.
Now, suppose this charge cloud moves. You have the same attractions and repulsions, but the nucleii have more mass per unit charge than the electrons in the cloud, so they will take a bit of time to react. The induced positive charge region will then lag behind the negative cloud, and will tend to drag it back. If you had a second negative cloud following some way behind the first one, it might be attracted towards this positive region.
If you had two conduction band electrons with long deBroglie wavelengths, with the same sorts of velocities and at the right distance apart, then you can get this sort of action. Over a limited range, you can get electrons to apparently attract each other, via electron-phonon iteraction.
This pairing up of electrons is pretty weak. If this was the only thing holding them together then you would not get superconductivity in ordinary materials above a few millikelvin. However, one they start organizing like that, then they can all tend towards a lowest energy state, where they are all moving like a single enormous particle, with a wavelength that is so much larger than most of the usual things that scatter electrons. A more electrons join this single state, an energy gap opens up betweeen the electrons that are in the state, and the ones that aren't, and it becomes more energetically tempting for other electrons to go with the flow. This energy gap stabilizes the superelectron state, and lets superconductivity happen at kelvin rather than millikelvin.
We have lots of particles giving off heat, but it isn't solidification. We don't have electrons standing shoulder to shoulder like soldiers. One superelectron's wave will significantly overlap hundreds or thousands of other superelectrons. If they had rigid orientations, then a supercurrent could not flow down a wire that got thinner, any more than your cheese with holes in it could flow down a funnel. Also, the electron-phonon coupling only binds if the electrons move. So, forget marching soldiers, unless you have soldiers that can see what is happening a hundred ranks ahead, and automatically calculate a path that will give zero jostling with their neighbours. It is not really a state that exist in the macroscopic world, but you can sort of guess what it might be like: everyone been cool and mellow and getting along with their neighbour, until one guy borrows the lawnmower without asking, or drinks the last beer in the fridge, and then it all suddenly collapses.
Okay, now if I get the article, you can get the same sort of thing with holes in a superfluid. The helium atoms can form a similar cooperating superfluid. The forces that balance to keep the atoms flowing in a coordianted fashion are different, but the principle is the same. If the particules are moving, and enough of their fields overlap, then there will be a lowest energy state, and one enough of them have discovered it, and particles can find it faster than random thermal fluctions can chuck them out, then everhting moves smoothly.
Helium atoms as lots of little round fuzzy things. Normally they overlap with lots of their neighbours. As you squish two of them together, the repulsive nuclear forces starts to rise sharply. The strong repulsive forces from the nearest neighbours will be bigger than the others, and wil
The apparent healing of the crack that you witness is not due to flow of the material, but rather chemical attack. When you score the glass you get 2 free surfaces with unsatified bonds. These bonds are rapidly satisfied by atmospheric molecules; mostly, water or hydroxyls. These molecules have a corrosive effect of the glass surface. Over time, the once atomically sharp crack-tip is blunted by this corrosion mechanism and the glass is effectively strengthened.