Mercury-containing oxides offer new perspective on mechanism of superconductivity

Apr 15, 2011
Figure 1: The crystal structure of HgxReO3. The mercury (Hg) atoms are shown in blue, oxygen (O) in red and rhenium (Re) in brown. Credit: 2011 The American Physical Society

(PhysOrg.com) -- To diversify the applications of superconductors that currently operate at chilly temperatures below 135 kelvin (K), scientists are searching for new classes of superconducting materials that will show this property at warmer temperatures. Now, a research team in Japan has synthesized a promising new class of superconductors1, made of Hg0.44ReO3, where an unusual motion of the mercury (Hg) atoms enhances superconducting properties at temperatures up to 7.7 K.

The Dutch physicist Heike Kamerlingh Onnes discovered one hundred years ago, when he noticed that the of mercury dropped to zero suddenly at 4.2 K. are now used routinely in scanners.

In classical superconductors such as mercury, superconductivity arises through the combined vibrations of the atoms in the crystal. This makes the crystal structure a key factor for the superconducting properties of a material. In the case of HgxReO3, the consists of rhenium (Re) and oxygen (O) building blocks. In the empty spaces between them, the mercury atoms arrange in chains (Fig. 1). However, some of the available places along these chains lack mercury atoms, and the team’s work suggests that this leads to an arrangement of paired mercury atoms.

"These pairs move within the channel in an oscillatory motion known as rattling", explains team-member Ayako Yamamoto from the RIKEN Advanced Science Institute in Wako. The rattling vibrations provide a strong feedback for the electrons, and therefore reinforce superconductivity in the material. In comparison to a similar structure lacking mercury pairs, the superconducting temperature of Hg0.44ReO3 at 7.7 K is almost twice as high. "Despite remaining below the present record of 135 K for a superconductor, there is potential for improving operation temperatures", says Yamamoto. “The application of pressure increases the superconducting temperature to 11.1 K, and this could mean that for the right crystal structure further enhancement is possible.”

Yamamoto and her colleagues are now working to optimize the crystal structure further—for example, by replacing rhenium with other elements. A better understanding of the influence of the mercury atoms’ rattling motion may also provide better insight into the mechanism of superconductivity in such structures. “Mercury seems to be a magic element in superconductivity, not only for its role in Kamerlingh Onnes’ discovery, but also for the fact that mercury is part of the material with the highest known superconducting temperature, HgBa2Ca2Cu3Ox,” Yamamoto explains. "Once more, is playing a key role for new superconductors," she says.

Explore further: Mathematical description of relationship between thickness, temperature, and resistivity could spur advances

More information: Ohgushi, K., et al. Superconducting phase at 7.7 K in the HgxReO3 compound with a hexagonal bronze structure. Physical Review Letters 106, 017001 (2011). Article

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Macksb
1 / 5 (1) Apr 16, 2011
This is another instance of a theory that I have described in multiple posts on Phys Org...namely, that superconductivity arises from synchronized oscillations of various types, which in turn cause Cooper pairs to form. Cooper pairs are themselves coupled oscillators, paired in exactly antisynchronous fashion.

The key ingredients noted in this article are "combined vibrations," "oscillatory motion," "rattling" and "rattling vibrations." Those are all oscillations. In the 1960s, Art Winfree showed how oscillators have a tendency to synchronize in certain exact patterns. See also Steve Strogatz's work (Cornell, applied math)extending Art's ideas, and his popular book Sync. Or think of Christian Huygens and his synchronized oscillations. Or the Millenium Bridge--synchronized oscillations in the bridge, interacting with the pedestrians, caused the pedestrians to synchronize their motions antisynchronously to the bridge and each other. Result: grouped Cooper pairs of pedestrians.
beelize54
not rated yet Apr 16, 2011
Cooper pairs are themselves coupled oscillators, paired in exactly antisynchronous fashion.
It's just another description of Cooper pairs, consisting of phonon mediated spin-spin interactions. It doesn't explain, why some materials exhibit the superconductivity, whereas others not. And because the Cooper pair formation doesn't describe the high temperature superconductivity well, neither your theory will do.
Macksb
3 / 5 (2) Apr 16, 2011
Beelize: Thanks. Yes, it correctly describes Cooper pairs. That's a plus, not a minus. The value lies in the fact that it offers a different perspective, and ties in to another body of work--coupled oscillator theory--that is more developed in other fields (biology and math). Note also that phonons, which you properly cite, are themselves oscillations...not just random oscillations, but most likely synchronized in the case of superconductors.

As to HTS, your criticism would be better directed at BCS theory, which not only failed to predict HTS, but also predicted that any HTS was impossible. In contrast, coupled oscillator theory may be broad enough to explain super behavior in BCS, pnictides, cuprates, and so on. I don't believe in separate explanations for each one. The quest becomes more general--a search for oscillators of any type (including particular lattices and laser fields) that might cause the oscillations of electrons to synchronize in various boson-like ways.
KBK
not rated yet May 04, 2011
Beelize: Thanks. Yes, it correctly describes Cooper pairs. That's a plus, not a minus. The value lies in the fact that it offers a different perspective, and ties in to another body of work--coupled oscillator theory--that is more developed in other fields (biology and math). Note also that phonons, which you properly cite, are themselves oscillations...not just random oscillations, but most likely synchronized in the case of superconductors.
* * *


You got it, dude. Coupled exclusion bubbles based on polarization and oscillatory complement situations.

This is the easy or initial path to HTS. Germany went this way during WWII, IIRC. (See "Joseph Farrell Walter Gerlach" as a web search). They were researching 'the whole shebang' and that sort of thing comes along for the ride.

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