Suggesting that atoms in a solid can move or be transported through it seems as impossible as using a syringe to inject material into a billiard ball. It shouldn’t work. But it turns out to be possible under certain conditions in super-solid helium, as demonstrated in scientific testing by UMass Amherst experimental physicist Robert Hallock and his doctoral student Michael Ray, in which atoms are added to a solid.
As the theoreticians Svistunov and Prokofiev explain, supersolidity is somewhat analogous to superconductivity, which is the total lack of electrical resistance that occurs in metals held at very low temperatures. This phenomenon is harnessed today in magnetic resonance imaging machines, for example, where superconducting magnets transport an electric charge, that is electrons, without friction.
This same “superflow,” or supersolidity, was first predicted to occur in a non-metal solid in 1969 by several prominent theoretical physicists who said a solid also should conduct its own atoms without friction when held at sufficiently low temperatures. They proposed helium 4 as a candidate element for observing this in the laboratory. Although early experiments failed to support the existence of super transport in a solid, later work in several laboratories reignited interest.
Svistunov says, “We now know for sure that supersolidity does exist in helium 4, although in a form very different from what was expected in the original theoretical work, and with side effects going far beyond mere super transport.” He and colleagues base this confidence on their first-principles studies of regular and disordered solid helium, using a significant advance in computational science called the “worm algorithm” proposed by them in 1998 and recently applied to helium.
It turns out that a key to supersolidity lies in the nature of the solid. As Svistunov explains, “Our simulations clearly show that a perfect helium 4 crystal is not a supersolid. But we find that certain imperfections, called dislocations, have a superfluid core and thus can demonstrate super transport. This is a possibility first envisioned about 20 years ago by Sergey Shevchenko and it was demonstrated by UMass Amherst experimental physicists Robert Hallock and Michael Ray in 2008.”
According to Svistunov and Prokofiev, Hallock and Ray conducted the first and still unique direct experimental observation of super transport in solid helium 4 in an apparatus Svistunov has dubbed the “UMass sandwich.” It has two reservoirs of liquid helium, each connected by a rod of helium-filled porous Vycor glass to a sample of solid helium 4 kept at 459 degrees below zero Fahrenheit and pressurized to 26 atmospheres. The physicists create a temperature gradient of about 3 degrees across each of the Vycor rods, which keeps the two reservoirs liquid while the solid sample remains a cold solid.
At 459 degrees below zero and high pressure, helium normally wants to be solid, but the tiny pores in the Vycor rods allow the helium atoms to remain in the liquid state. The setup prevents atoms from solidifying despite the temperature and pressure and allows liquid-solid contact at the boundary between helium-filled Vycor and the solid helium, Hallock explains.
“We feed some helium atoms into one reservoir, and we then see an increase in pressure in the second reservoir, which is connected to the first only by a pathway through the Vycor rods and solid helium 4. Below a specific temperature we clearly observe that atoms move from one reservoir to the other through the solid helium, but at higher temperatures they do not. The question is how this super transport can happen.”
To date, according to Hallock, the remarkable observations so far rule out many mundane explanations. More importantly, the UMass Amherst experiments so far do not exclude the possibility that something quite remarkable is taking place, as Svistunov and Prokofiev propose. Hallock notes, “Everything observed so far is consistent with Boris and Nikolai’s predictions. While there are more tests to do, so far we have not refuted their ideas.” He adds that even more striking than the supersolidity per se is the so-called effect of giant isochoric, or constant-volume, compressibility that always is present when flow is observed in the experiment.
Basing their theory on first-principles simulations, Prokofiev, Svistunov and colleagues argue that this bizarre effect is due to a synergy between superfluidity in the cores of imperfections known as dislocations and the known ability of dislocations to “climb,” that is, grow under conditions when mass flow is provided to their cores. There are no practical implications of Svistunov and Prokofiev’s numerical model at present, but as Svistunov observes, “Sooner or later a good theory will become practical. And because we’ve used an unbiased, first principles approach, this work is very meaningful for helping us to understand some of the fundamental properties of quantum matter.”
Svistunov, Prokofiev and Soyler collaborated with colleagues at Harvard and the City University of New York on their recent publication.
Boris Svistunov | Newswise Science News
Pulses of electrons manipulate nanomagnets and store information
21.07.2017 | American Institute of Physics
Vortex photons from electrons in circular motion
21.07.2017 | National Institutes of Natural Sciences
Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.
For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...
What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.
To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...
The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....
A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...
Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision
Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...
21.07.2017 | Event News
19.07.2017 | Event News
12.07.2017 | Event News
21.07.2017 | Earth Sciences
21.07.2017 | Power and Electrical Engineering
21.07.2017 | Physics and Astronomy