Supersolidity

Letter

 

Eugene Sittampalam

 

Liquid 4He enters the superfluid state and flows without friction below 2.176 K. Thin liquid films adsorbed on solid substrates undergo the same transformation, although at a lower temperature. When the substrate is subjected to oscillatory motion a portion of the film, known as the superfluid fraction, decouples from the oscillation. A similar phenomenon has been observed1, 2 in solid 4He, in which a fraction of the solid seems to decouple from the motion of the surrounding lattice. Although this observation has been replicated in various laboratories3, 4, 5, 6, no thermodynamic signature of the possible supersolid transition has been seen. Here we report the finding of a heat capacity peak that coincides with the onset of mass decoupling. This complementary experimental evidence supports the existence of a genuine transition between the normal solid and supersolid phases of 4He.

Probable heat capacity signature of the supersolid transition, X. Lin, A. C. Clark & M. H. W. Chan (Pennsylvania State University), Nature 449, 1025-1028 (2007)

 

The apparent observation of supersolid helium in 2004 generated much interest in the physics community, and curiosity outside of it. But the thermodynamic signature expected to accompany the transition was absent. Lin et al. present new evidence on the matter. The phenomenon, which shows similarities to that seen when liquid helium enters the superfluid state, occurs when a fraction of the solid appears to decouple from the motion of the surrounding lattice. The new experiment reveals a heat capacity peak coincident with the onset of mass decoupling, which supports the existence of a genuine transition between the normal solid and supersolid phases of 4He.

Supersolid signature, Nature, Editor's Summary, 25 October 2007

 

In recent years, no topic in condensed matter physics has been hotter than the study of ultracold solid helium. Subtle experiments suggest that as temperatures dip toward absolute zero, crystalline helium can bizarrely flow like a liquid with no viscosity, a phenomenon known as supersolidity. Now, a new experiment lends credence to that controversial claim by revealing a possible second sign of the transition.

The first evidence for supersolidity emerged in 2003 and 2004. Moses Chan and Eun-Seong Kim of Pennsylvania State University in State College filled a tiny can with liquid helium and squeezed the ultracold stuff to greater than 25 times atmospheric pressure to make it solidify. They then set the can twisting back and forth on top of a thin shaft. Below a temperature of about 0.2 kelvin--2/10 of a degree above absolute zero--the frequency of the twisting shot up as though the can had become less massive. That implied that some of the helium had let go of the can and was standing stock-still while the rest of it continued to twist back and forth. That in turn suggested that the solid helium was flowing through itself without any resistance, a phenomenon known as supersolidity that had been hypothesized in the 1960s (Science, 1 July 2005, p. 38).

But some believed that Kim and Chan had observed less-mysterious "superfluid" liquid helium wending its way through cracklike defects in the crystal. That alternative interpretation got a shot in the arm in 2006, when Ann Sophie Rittner and John Reppy of Cornell University claimed that they, too, had seen the phenomenon but could make it go away by gently heating and cooling the solid helium to smooth over defects in the crystal (ScienceNOW, 15 March 2006).

Now, Chan and colleagues Xi Lin and Anthony Clark have new results that suggest supersolidity may be a property of the solid crystal after all. If that were true, then the onset of supersolidity ought to be a "thermodynamic phase transition," much like the freezing of water into ice or the emergence of magnetism in hot iron as it cools. During such transitions, the heat capacity of a material--the amount of heat required to raise the temperature of the stuff--increases dramatically. And that's what Chan and colleagues see in solid helium, they report this week in Nature.

Technically, this was no small feat. The heat capacity of the helium is much smaller than that of the metal container holding it. So to spot the peak, the researchers had to use a special container fashioned out of silicon and take precautions to prevent any unaccounted heat leaks. Chan cautions that the team hasn't yet proved that the heat-capacity signal, which actually occurs at a slightly lower temperature than the onset of flow, is tied to supersolidity, however. "That's why we use the word 'probable,' " he says, "in case there is another explanation."

But if the peak is really there, it bolsters the case that supersolidity involves a real phase transition, says experimenter Norbert Mulders of the University of Delaware, Newark. However, he adds, "I have a pretty good idea of how difficult these measurements are, so it would probably take [confirmation by] some competing experiment to completely convince me."

Evidence for "Supersolidity" Becomes More Solid, Adrian Cho, ScienceNOW Daily News, 24 October 2007

 

 

– Letter –

 

To:          chan@phys.psu.edu

Cc:          nature@nature.com, “Adrian Cho” <science-now@aaas.org>

Subject:   Nature 449, 1025-1028 (2007)

Date:       24 November 2007

 

Drs M H W Chan, X Lin & A C Clark

Department of Physics

The Pennsylvania State University

 

Dear Learned Researchers,

Probable heat capacity signature of the supersolid transition

In reference to your above Letter, please be good enough to access (1) and (2) for perusal. You may find them to be of fundamental interest and an indispensable backdrop to your continuing research.

 

The heat capacity peak you report here (in the transition between the normal solid and supersolid phases of 4He) should also correspond to an equivalent peak in the mass content of the material. This would not only be affirmative to your report but also be in accordance with the final perspective on the nature of things, as introduced in (2). (The individual 4He atoms in the supersolid would act as perfect ball bearings, with their centers at relative rest in the crystal lattice.) Hope there's a way of precisely measuring this mass (or weight) difference here as well, next!

A further verification that follows from your experiment is that of absolute space, as defined in (2). Decoupling from its surroundings, the supersolid would eventually come to rest in the lab frame – but oriented in the direction the lab is moving in absolute space, or the absolute reference frame; and this orientation should ideally revolve through a full cycle every 24 hours in the lab!

 

Finally, it may also be noted that the response from Physics World to the submission of (2) has since been negative, leaving the monetary offer therein for its refutation still open! Would your physics department head at PSU kindly consider being the moderator here (holding the cash in hand!)? Moderator's fee, too, will be paid by me in advance. No joke; no scam; just an earnest appeal to you to resolve this matter for me early with your profound knowledge and expertise. (The money offered is the least I could do in gratitude. It would be worth every penny for me considering the time I would otherwise be wasting in trying to flog a fundamentally flawed worldview.)

Any feedback would be gratefully received.

Thank you and all the very best in your continued quest for answers.

Sincerely,

Eugene Sittampalam

www.sittampalam.net

 

(1) www.sittampalam.net/Superconductivity.htm

(2) www.sittampalam.net/LateralThoughts.pdf

 

– End of Letter –

 

 

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