A spiral through frozen helium

A spiral through frozen helium:

This spiral is a crystal of silicon carbide, made during an experiment conducted in 2007...

There are flaws in the crystal, and, when the mixture reached a certain temperature and pressure, the solid helium turned to a superfluid.

...The crystal of frozen helium was twisted around, and suddenly the twisting got easier, as if some of the mass had disappeared.

Existential blow for ghostly quantum supersolids - New Scientist - New Scientist

Existential blow for ghostly quantum supersolids - New Scientist: ...they sealed the glass with a thin layer of epoxy resin and inserted the helium through a very thin tube. This meant only a tiny fraction of the helium could become a bulk solid – and so any speeding up due to quantum plasticity would be negligible.

Chan and Duk Kim found that this set-up completely eliminated the changes in oscillation rate that they had originally observed. "We didn't see anything at all," says Chan. That suggests that all of the speeding up in the original experiment must have been due to bulk helium forming a quantum plastic, not supersolidity as originally claimed in 2004.

Superstuff: When quantum goes big

Superstuff: When quantum goes big: Imagine you have two identical particles, and you swap their positions. The physical system looks exactly the same, and responds to an experiment exactly as before. However, quantum theory records the swap by multiplying their quantum state by a "phase factor". Switching the particles again brings in the phase factor a second time, but the particles are in their original position and so everything returns to its original state. "Since switching the particles twice brings you back to where you were, multiplying by this phase twice must do nothing at all," says John Baez at the Centre for Quantum Technologies in Singapore. This means that squaring the phase must give 1, which in turn means that the phase itself can be equal to 1 or -1.

Shaking down frozen helium: In a 'supersolid' state, it has liquid-like characteristics

Shaking down frozen helium: In a 'supersolid' state, it has liquid-like characteristics: In fact, in this paper, the researchers show instead a more prosaic explanation: There are moving defects in the solid helium crystals, and their relaxation time falls with rising temperatures. This is more consistent with the torsional oscillation (shaking) experiments conducted at Cornell.
The researchers learned that the unusual properties of solid helium do not reflect a clunky transition between the solid state and a supersolid state. It behaves like a dimmer switch and presents a smooth transition near absolute zero.

Shaking down frozen helium: In a 'supersolid' state, it has liquid-like characteristics

Shaking down frozen helium: In a 'supersolid' state, it has liquid-like characteristics: In fact, in this paper, the researchers show instead a more prosaic explanation: There are moving defects in the solid helium crystals, and their relaxation time falls with rising temperatures. This is more consistent with the torsional oscillation (shaking) experiments conducted at Cornell.
The researchers learned that the unusual properties of solid helium do not reflect a clunky transition between the solid state and a supersolid state. It behaves like a dimmer switch and presents a smooth transition near absolute zero.

Experimental evidence adds to the likelihood of the existence of supersolids, an exotic phase of matter

Experimental evidence adds to the likelihood of the existence of supersolids, an exotic phase of matter: The reduction in the rotational inertia of a bar of solid helium-4 as it was cooled to very low temperatures provided the first experimental evidence for supersolids. Physicists interpreted the reduction to mean that some amount of supersolid helium had formed and decoupled from the remainder of the bar, affecting its rotational inertia and frequency. Others argued that the reduction in inertia resulted from a change in the helium’s viscosity and elasticity with temperature, rather than from the onset of supersolidity.

New evidence that weird quantum supersolid exists - physics-math - 18 November 2010 - New Scientist

New evidence that weird quantum supersolid exists: He suggested that the reason the cylinder switched more quickly at lower temperature was because the helium had become a wobbly "quantum plastic", a previously unknown phase of matter that is distinct from a supersolid. The increased elasticity of this new material allowed the cylinder to more easily reverse its rotation, he said.

To test whether Reppy was right, Kim spun the larger apparatus in which the cylinder sits: the apparatus spun in just one direction, while the cylinder spun one way, then the other, as it had before. He reasoned that elasticity should affect only how quickly the cylinder switched direction, not its actual spinning rate. Therefore if Reppy was right, and the solid helium was a quantum plastic, adding a constant underlying rotation should not change the results.

His team found, however, that it did. Unlike in the original experiment, the direction switches did not get faster with a falling temperature.

A Matter Of Solidity - Science News

A Matter Of Solidity - Science News: "The breakthrough came after John Goodkind of the University of California, San Diego reported that sound waves traveled in an unexpected manner through solid helium. Intrigued, Moses Chan of Pennsylvania State University in University Park decided to launch a new study of solid helium using a device called a torsional oscillator. This machine oscillates a sample back and forth around a central axis, like a merry-go-round spinning first one way and then the other at 1,000 times a second.

Such oscillators had been used to hunt for superfluidity because quantum materials, when placed in a spinning container, don’t spin along. Imagine rotating a bucket of water. If the water were a superfluid, it wouldn’t slosh around with the rotation but would instead sit unmoving, decoupled from the bucket’s moving sides. Supersolids, if they exist, would do the same thing. Thus, as a solid transitions to a supersolid state at low temperatures, the period of time it takes for the oscillator to rotate back and forth would drop — because less mass would be sloshing around."

Evidence for Free-Flowing Supersolid Slipping Away? -- Cho 329 (5987): 20 -- Science

Evidence for Free-Flowing Supersolid Slipping Away? -- Cho 329 (5987): 20 -- Science - "Six years ago, frigid solid helium set the world of condensed-matter physics afire when one team found that at temperatures near absolute zero the stuff appears to flow like a liquid without any viscosity (Science, 1 July 2005, p. 38). Physicists have since debated how such "supersolidity" might come about, or whether it even exists. Now, an experiment calls into question the first, best evidence for supersolidity. What physicists took as a sign of resistance-free flow at very low temperatures is in fact a manifestation of an odd softening of the solid at slightly higher temperatures, says John Reppy of Cornell University."

Ghostly, flowing supersolid? No, it's quantum plastic - physics-math - 30 June 2010 - New Scientist

Ghostly, flowing supersolid? No, it's quantum plastic - physics-math - 30 June 2010 - New Scientist: "He concludes that the link between temperature and oscillation frequency is down to a totally new quantum effect, not supersolidity. This new effect, Reppy says, occurs due to the defects inherent in all solid helium-4, which change their behaviour at different temperatures."

Quantum wonders: Superfluids and supersolids

At very low temperatures, the momentum of individual atoms or electrons in these materials is tiny and very precisely known, so the position of each atom is highly uncertain. In fact, they begin to overlap with each other to the point where you can't describe them individually. They start acting as one superatom or superelectron that moves without friction or resistance.

Quantum wonders: Superfluids and supersolids - physics-math - 09 May 2010 - New Scientist

Evidence mounts for an exotic supersolid

Rubidium atoms simultaneously act like a solid and a superfluid

http://www.sciencenews.org/view/generic/id/41869/title/Evidence_mounts_for_an_exotic_supersolid

Cracking the supersolid

A supersolid is one of the truly enigmatic quantum states of matter, whereby atoms that remain locked in crystalline order can also resist rotation if the crystal is rotated.

http://www.sciencemag.org/cgi/content/full/sci;316/5830/1435

Superfluidity of Grain Boundaries and Supersolid Behavior

When two communicating vessels are filled to a different height with liquid, the two levels equilibrate because the liquid can flow. We have looked for such equilibration with solid ⁴He. For crystals with no grain boundaries, we see no flow of mass, whereas for crystals containing several grain boundaries, wedetect a mass flow. Our results suggest that the transport of mass is due to the superfluidity of grain boundaries.

http://www.sciencemag.org/cgi/content/full/313/5790/1098

Physicists See Solid Helium Flow, But Not in the Most Exciting Way

... Sébastien Balibar of the École Normale Supérieure in Paris and colleagues have seen the flow ofsolid helium--but only in imperfect crystals consisting of several distinct "grains." That suggests a less exotic explanation for the flow: On the boundaries between grains, the helium remains inherently liquid, and superfluid liquid helium, which also flows without resistance, seeps along the interfaces...

http://www.sciencemag.org/cgi/content/full/sci;313/5787/603a?maxtoshow=&hits=10&RESULTFORMAT=&fulltext=solid+helium+flow&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT