No Supersolid In New Experiment

OK, there are two separate issues here.

First, a new experiment, done by the person responsible for the first announcement of the possible discovery of supersolid, has now shown no evidence for that.

Many other theoretical and experimental results finally convinced Chan to redo the experiments. With postdoctoral researcher Duk Kim, he completely redesigned the torsional oscillator, taking every precaution to eliminate space for elastic helium. This time, the changes in oscillation previously attributed to a supersolid state were completely absent.

Chan realizes that this almost closes the book on supersolid helium. ”I’m in an awkward position, since we started the whole damn thing,” says Chan. “But I’m glad we were the ones who found the explanation.” Beamish agrees that these are extremely subtle effects, which is why it took so long to sort them out: “I give Moses the greatest credit for all the years he spent trying to find out what it was, rather than trying to prove it was what he said it was.” He also notes that the hunt for supersolids actually seeded new research on what has become known as quantum plasticity—the tendency of a material to deform macroscopically based on its quantum properties.

Which brings me to my second issue here of the utmost respect we all should have to Moses Chan for illustrating what a true scientist should do when faced with a contradicting evidence. Here is a person who received quite a coverage and reception when the first supersolid discovery was announced. Yet, he continues to investigate the effects in light of the responses he got, and now, after redoing the experiment and found that his original conclusion was wrong, he went ahead and published it! (Taleyarkhan, are you paying attention to all this?)

Have any religious leaders nowadays done such a thing? And yet, there are still people out there who insist that science is a religion?

Zz.

"Supersolids: What and Where Are They?"

This is a review paper on supersolids that will be published in Rev. Mod. Physics, so you get to see and read it right now. It should address all the questions you have on supersolids, but were afraid to ask!

:)

Zz.

No Supersolid Yet?

Another wrench has been thrown into the claim of experimental observation of supersolids. A new paper in PRL[1] is throwing doubt into such observation, and in fact, attribute the apparent observation to quantum plasticity.

Looks like a lot more work needs to be done to verify if we truly have a supersolid in such a system.

Zz.

[1] J. D. Reppy Phys. Rev. Lett. 104, 255301 (2010).

Is It a Gas, Fluid, Solid, or All of the Above?

A surprising and fascinating report coming out of the on-going APS March Meeting. A group from Berkeley is reporting the possible discovery of a supersolid in "... a gas of rubidium atoms..."!

To look for this ordering, Stamper-Kurn's team used a conventional laser trapping technique to confine a gas of millions of rubidium atoms in an oblong, surfboardlike trap. They then cooled the sample to below 500 nanokelvin. Lastly, they hit their collection of rubidium atoms with a beam of circularly polarized light, which is reflected differently by atoms with a different magnetic orientation and can, therefore, reveal the magnetic orientation of the atoms in the sample. What they saw was that within their optical trap, the rubidium atoms ordered themselves into an array of 5-micrometer-square domains, inside which all of the atoms adopted a similar magnetic orientation. What's more, these domains adopted a crystalline-like ordering, with alternating domains with different magnetic directions. This ordering wasn't perfect like the regular lattice of sodium and chlorine atoms in table salt. But it's not random either (see picture). "There is some emergent order which shows up in this system," Stamper-Kurn says.

Once the Berkeley researchers spotted the ordered makeup of the atoms, they decided to check whether the gas was coherent as well. Using another laser, they nudged two groups of rubidium atoms already in their trap. They found that the atoms interfered with each other in the same way that two coherent light beams create an interference pattern of light and dark stripes, an unmistakable sign of their wavelike quantum nature.

Amazing!

This appears to have a stronger and more definitive observation than the earlier report of possible supersolid state in solid He. It should be quite interesting to see if this gets verified, especially in having the ordered state to qualify as a "solid".

Zz.

Major Physics Breakthrough In Understanding Supersolidity

I guess one of the major news of this week is the new discovery of the sheer modulus characteristic of a He in the "supersolid" phase[1] (assuming that it did become a supersolid).

Day and Dr. Beamish have taken this research a different direction. In an experiment not done before, they cooled the solid helium and manipulated the material another way -- by shearing it elastically. In doing so, they found that the solid behaved in an entirely new and unexpected way -- it became much stiffer at the lowest temperatures.

A perspective of this work in Nature[2] has a bit more info:

A supersolid can exhibit other anomalies, for instance in the speed at which sound passes through it. Sound speed depends on the shear modulus of the solid, as well as the density of the superfluid component. To assess why the solid behaves in the way it does, it is thus important to measure the shear modulus independently of the superfluid density. This is precisely what Day and Beamish have now done with solid helium.

Again, the authors' experiment3 is conceptually simple. They placed solid 4He between two parallel plates, known as piezoelectric shear transducers. They moved one plate, the driving transducer, in a direction parallel to the second plate. The solid helium transmits the resulting elastic shear stress between the plates, and this is measured by the second transducer. Day and Beamish find3 that the shear modulus of helium rises by up to 10% as the temperature is reduced from 0.2 to 0.02 kelvin. More significantly, the temperature dependence of this large increase in shear modulus closely tracks the changes in period in the torsional-oscillator experiments.

Fascinating stuff coming out of supersolidity lately.

Zz.

[1] J. Day and J. Beamish, Nature v.450, p.853 (2007).
[2] A.T. Dorsey and D. A. Huse, Nature v.450, p.800 (2007).

Cracking the Supersolid

Did you read the terrific overview on the issues surrounding the "supersolid" written by Phil Phillips and Alex Balatsky (Science, vol. 316, 1435 (2007)). If you did, they have uploaded what they say is an extended version of that article. So you may want to read this even if you already read the Science version.

Zz.