How to maximize the superconducting critical temperature in a molecular superconductor

April 17, 2015, Tohoku University
The fullerene molecules consist of 60 carbon atoms arranged in a truncated icosahedral shape (a soccer ball) and pack in a regular cubic-close-packed array in three dimensions. Alkali metal ions (blue spheres) occupy vacant interstitial holes of octahedral and tetrahedral symmetry. Credit: Prassides Kosmas

An international research team, led by Professor Kosmas Prassides of Tohoku University, has investigated the electronic properties of the family of unconventional superconductors based on fullerenes which have the highest known superconducting critical temperature (Tc) among molecular superconductors.

In results published in the American scientific journal Science Advances, the team was able to demonstrate the guiding influence of the molecular electronic structure in controlling superconductivity and achieving the maximum Tc, opening the way to new routes in the search of new molecular superconductors with enhanced figures of merit.

Background:

Metals are used for electricity transmission, but energy is lost as heat because of . Superconductors have no electrical resistance and can carry electricity without losing energy, so it is important to find superconductors which can work at the highest possible temperature.

Most superconductors have simple structures built from atoms. But recently, superconductors made from molecules arranged in regular solid structures have been found.

Work by members of the team on molecular fulleride-based systems has previously led to the discovery of the highest working temperature (at 38 K) for a molecular superconductor (Nature Materials 7, p. 367, 2008).

The electronic ground state, which is in competition with superconductivity, was found to be magnetically ordered (Science 323, p. 1585, 2009). And the zero-resistance superconducting state could be switched on by tuning the exact arrangement of the C60 molecules in the solid by external pressure (Nature 466, p. 221, 2010).

These are schematic depictions of the Jahn-Teller molecular distortion of the fullerene units in the Mott-Jahn-Teller insulator (blue molecules) and the Jahn-Teller metal (yellow molecules), their respective molecular electronic structure (lifting of the orbital degeneracy due to the distortion), and the resulting intermolecular hopping of the electrons (prohibited in the insulator, weak hopping in the Jahn-Teller metal). This situation contrasts with the behavior of the conventional metal where hopping is allowed, the orbital degeneracy is retained, and the molecules are undistorted (green molecules). Credit: Prassides Kosmas

The controlling role of the molecular electronic structure was then identified by demonstrating that the parent insulating state involves Jahn-Teller distortion of the molecular anions that produces the magnetism from which the superconductivity emerges (Nature Communications 3, 912, 2012).

Breakthrough:

The research team has addressed for the first time the relationship between the parent insulator, the normal metallic state above Tc and the superconducting pairing mechanism in a new family of chemically-pressurized fullerene materials. This is a key question in understanding all including the high-Tc cuprates, the iron pnictides and the heavy fermion systems.

Electronic phase diagram of face-centered-cubic (fcc) structured fullerides shows the evolution of the superconducting transition temperature, Tc (superconductivity dome) and the Mott-Jahn-Teller insulator to Jahn-Teller metal crossover temperature, T' as a function of volume per C60. Within the metallic (superconducting) regime, gradient shading from orange to green schematically illustrates the Jahn-Teller metal to conventional metal (unconventional to weak-coupling BCS conventional superconductor) crossover. The inset shows the crystal structure of fcc A3C60 fullerides (A=alkali metal, green spheres represent cations on tetrahedral and red on octahedral holes, respectively). Credit: Prassides Kosmas

Their work unveiled a new state of matter - the Jahn-Teller metal - and showed that when the balance between molecular and extended lattice characteristics of the electrons at the Fermi level is optimized, the highest achievable temperature for the onset of is attained.

As synthetic chemistry allows the creation of new molecular electronic structures distinct from those in the atoms and ions that dominate most known , there is now strong motivation to search for new molecular superconducting materials.

Explore further: A potential Rosetta stone of high temperature superconductivity

More information: Science Advances, vol. 1, article number: e1500059, 2015 . DOI: 10.1126/sciadv.1500059

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13 comments

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Da Schneib
not rated yet Apr 18, 2015
And the road to superconducting thread opens.

I think it's about time to start figuring out the maximum current density superconducting fibers can sustain. There will be a limit, and we need to have the math to say what it is.
redge_little
not rated yet Apr 18, 2015
RBL first correctly propsed (Dec 2005) a model for high temperature superconductivity based on spin induced changes in bond symmetry by the Little Effect for superconducting to magnetic phase changes that are indentical to this Jahn Teller type phases transformations. See Page 19 of "a Theory of Relativistic spinrevorbital [ http://www.academ...AB049585 } ; click 'full Text PDF' for a free download of the manuscript. Now an international team of scientists experimentally observe such mechanism in alkali fullerides of the same nature as my prior model.
redge_little
not rated yet Apr 18, 2015
In a short recent article (http://arxiv.org/abs/1412.4012 ) , I applied such model to fullerides and graphene oxide to explain superfluidity through graphene oxide membranes and provide a unified model of superconductivity and superflluidity and even explain trends in Tc among various materials and provide a material basis for raising Tc well beyond room temperature!
Da Schneib
5 / 5 (1) Apr 18, 2015
Anything actually get published, or is this just more abuse of arXiv?
redge_little
1 / 5 (1) Apr 19, 2015
I think my manuscript is not an abuse of arXiv so long as my manuscript with its concepts and theory is consistent with many subsequent findings of other scientists on different topics using different experimental approaches and high level calculations from many different countries. In the last year I have not actively been involved in publishing it. But the sad scenario is that with hundreds of subsequent support from the many subsequent work of others it is really bad that it has not been published! Who ever you are, if the work was found to be not true by experiment then I would consider it abuse and even write a new manuscript to that effect. But the reality is that it works well against the test of others. A theory that is grounded in subsequent experiments is certainly not abuse!
docile
Apr 19, 2015
This comment has been removed by a moderator.
Da Schneib
not rated yet Apr 20, 2015
I think my manuscript is not an abuse of arXiv
Another nutjob making a mess of what otherwise might be a useful scientific resource, wasting taxpayer money and spreading more disinformation.

There is no need to invent new stuffs
Then where are all the superconducting transmission lines? Just askin'.
docile
Apr 20, 2015
This comment has been removed by a moderator.
redge_little
1 / 5 (1) Apr 20, 2015
Hi Da Schneib,
Expressing truth as best known is not the work of what you call a 'nutjob' whatever that is. And such new ideas and concepts contribute to mankind and are in no way a waste of taxpayers' money! Such concepts and ideas as expressed in the quoted manuscript are not only the views of the author but since Jan 2014 many other scientists have archived and published similar consistent ideas. But you are entitled to your own beliefs. I think it best that you exist in your beliefs and leave me out of them! I wish not to discuss this more with you!
Da Schneib
not rated yet Apr 20, 2015
Then where are all the superconducting transmission lines? Just askin
It's like to ask, where are all these nice graphene or quantum computer applications? We have working theories for them thirty years already. The existence of valid theory doesn't imply the existence of practical applications (and vice-versa).
So what's the bottom line? Are you claiming that this is a waste of time? It looks like new theoretical stuff from over here.

Also, it seems like once theory gets developed enough it just about always results in practical applications. Are you denying consilience?
Da Schneib
not rated yet Apr 20, 2015
When someone claims a new scientific discovery on a paper on arXiv and it never gets published, we all know what that means, redge.

Crank alert.
redge_little
1 / 5 (1) Apr 20, 2015
With all due respect to you Da Schneib, in some cases what you are thinking may be the case, ie crank! But there can be some underlying circumstances that reflect different scenarios. For example, the author may get disturbed in a way that does not allow the follow through on a profound discovery or observation. Unless one knows the details of the circumstances of the author it is prudent not to jump to irrational conclusions. This is simply an intellectual and moral point of view. In this case of "A Theory of the Relativistic Fermionic Spinrevorbital", if you are interested or positive in outlook, there have already been others who subsequently publish supporting manuscript ((http://arxiv.org/abs/1412.4012 ) after its disclosure. With Kind Sincerity, RBL
Da Schneib
not rated yet Apr 20, 2015
LOL, either they're irrational or they're not.

Make up your mind.

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