Superconductivity-like electron pair formation in molecules discovered

November 9, 2012

(Phys.org)—Usually, electrons try to avoid each other due to their electrostatic repulsion. On occasion, however, they can form a pair which has long been known in superconductivity called a "Cooper pair," named after the physicist who first described them. In work published in Physical Review Letters, researchers from the Wehlitz group at SRC outline their discovery that electrons can form pairs in some aromatic molecules as small as benzene.  A benzene molecule consists of only 6 carbon atoms in a ring with one hydrogen atom attached to each of them.

The benzene ring allows the electrons, when the molecule absorbs a photon with a certain amount of energy, to flow around in a ring-shaped orbital where they can form a 2-electron pseudo particle just like a Cooper pair.  This pair formation is, on the one hand, independent of the specific molecule (i.e. is the same for benzene naphthalene, anthracene) but, on the other hand, does not exist at all for other molecules like pyrrole (a pentagonal ring with four carbon and one nitrogen atom).

This finding opens a new avenue in the quest for understanding and, ultimately, in the search for . While benzene is not a superconductor, the data shows the formation of a Cooper pair, which is a requirement for superconductivity.  Thus benzene can be used as a convenient model system to study Cooper pair formation.

Explore further: Size matters - even for molecules

More information: PRL paper: prl.aps.org/abstract/PRL/v109/i19/e193001
Synopsis: physics.aps.org/synopsis-for/10.1103/PhysRevLett.109.193001

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PPihkala
not rated yet Nov 09, 2012
What is the smallest possible graphene flake? I think this benzene ring is that. Therefore it can have same properties as graphene, including low loss or lossless transfer of electrons.
johanfprins
1 / 5 (1) Nov 10, 2012
A Cooper pair is modelled to form by means of "phonon-exchange". I do not see any evidence for a phonon in this data.

What the authors miss is that a covalent bond is also pair-formation, without involving a phonon. So why do they call the electron-pairs they observe in a benzene ring a "Cooper pair". To call it the latter, they must first prove the involvement of a phonon in the formation of the pair. They have not done this!

In fact pair formation of electrons, without any phonon assistance, can be easily generated and has been known to occur since the time that Lewis explained the covalent bond.

In addition, superconduction DOES NOT require pair-formation: Electron-pairs (not those formed by the physically impossible Cooper mechanism), can act as charge-carriers during superconduction, but it is NOT mandatory that the charge-carriers MUST be electron-pairs for superconduction to occur.
ValeriaT
1 / 5 (1) Nov 10, 2012
A Cooper pair is modelled to form by means of "phonon-exchange". I do not see any evidence for a phonon in this data
In this article you're writing:
There is of course no reason, why these orbitals couldn't be bi-electron orbitals. In fact, they most probably will be... It will be now postulated, that oxygen atoms..supply electrons, which do form arrays of bi-electron orbitals..
Are you implying, they're forming arrays of Cooper pairs? If yes, why are you fighting against Cooper pair theory so obstinately? If not, in which these bi-electron orbitals differ from Cooper pairs? BTW do you realize, these bi-electron orbitals are way too small for being able to explain the supercritical islands observed in pseudogap state? I know, you're fighting with BCS theory all the time, but you're still maintaining a back-door for it here.
johanfprins
1 / 5 (1) Nov 10, 2012
]In http://arxiv.org/.../0607227 you're writing:
There is of course no reason, why these orbitals couldn't be bi-electron orbitals. In fact, they most probably will be... It will be now postulated, that oxygen atoms..supply electrons, which do form arrays of bi-electron orbitals..
Are you implying, they're forming arrays of Cooper pairs?

You have asked this same question on another thread and I have answered that the double-electron orbitals ARE NOT Cooper pairs since the "bonding" of electrons by phonon-exchange is a crackpot idea.

I am not going to answer the same questions on this thread; except to state that since I have written that article, I have come to the conclusion that doubly-charged charge-carriers are probably as rare as chicken teeth.

At that stage I still believed that flux qunatizaton and Josephson tunnelling prove doubly-charged charge-carriers. I now know that the models used for flux quantization and J-tunneling are wrong.
Minich
not rated yet Nov 23, 2012
I have found in original text of the article
"In this Letter, we report the discovery of the
formation of a single quasiparticle state, which can be
considered as a generalized Cooper pair, in benzene, naphthalene,
anthracene, and coronene, and its subsequent
emission from the molecule after photoabsorption."

It is too provocative statement. I guess there are more standard explanations for "the ratio of doubly to singly charged parent ions" such as momentum and energy conservation (photon momentum can be considered almost zero).

See for example raman scattering in superfluid helium 4, so called "two roton bound state".

Data presented are too raw, for example, i could not find words "polarized light"...

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