Extremely strong coupling superconductivity of heavy-electrons in two-dimensions

Oct 17, 2011
Fig. 1: Transmission elctron microscope image of the superlattice of alternating layers of one unit-cell-thick magnetic CeCoIn5 and five unit-cell-thick nonmagnetic YbCoIn5.

The ultimately strong electron-electron interaction in metal is realized in the so-called heavy-fermion compound containing rare earth elements, in which the electron effective mass is enhanced by a few hundred times the free electron mass.

The group of Yuta Mizukami, Yuji Matsuda and Takasada Shibauchi in Department of Physics and Takahito Terashima in Research Center for and Materials Sciences, has succeeded in achieving the first experimental realization of ‘heavy superconducting electrons’ in a two-dimensional lattice, which were obtained by fabricating heterostructures unavailable in nature.

Superlattices with heavy-fermion CeCoIn5 and nonmagnetic YbCoIn5 layers are grown alternately by the molecular-beam-epitaxy technique (Fig. 1). Superconductivity is observed even in superlattice with one-unit-cell thick CeCoIn5 layers, demonstrating a heavy-electron superconductivity with purely two-dimensional electron correlations.

Fig. 2: Superconducting properties of CeCoIn5/YbCoIn5 superlattices. Left: Temperature dependence of the resistivity. n is the number of CeCoIn5 layers. Right: Thickness dependence of the superconducting transition temperature and the superconducting coupling strength, represented by 2Δ/kBTc. In most superconductors, the 2Δ/kBTc value is close to 3.5.

Most remarkably, the superconductivity in superlattices persists under significantly higher reduced magnetic fields than in the bulk, implying that the force ("glue") holding together the superconducting electron pairs takes on an extremely strong coupled nature as a result of two-dimensionalization (Fig. 2) -- a situation reminiscent of the high-Tc cuprates.

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More information: The article, " Extremely strong coupling superconductivity in artificial two-dimensional Kondo lattices " by Y. Mizukami, H. Shishido, T. Shibauchi, M. Shimozawa, S. Yasumoto, D. Watanabe, M.Yamashita, H. Ikeda, T. Terashima, H. Kontani, Y. Matsuda was published in Nature Physics. Published online 09 October 2011. DOI:10.1038/nphys2112

Provided by Kyoto University

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3.7 / 5 (3) Oct 17, 2011
This result is consistent with a theory that I have posted several times on PhysOrg. I believe the glue or force is simply a case of Art Winfree's theory of coupled oscillators. In 1967, Art showed that limit cycle oscillators have a tendency to couple. His work was extended by Kuramoto, Strogatz, Mirollo and others. See Sync, by Strogatz.

Art applied his theory mainly to biology (heart cells, Malaysian fireflies, etc.) More recently, Strogatz and Mirollo have stressed that it must apply to physics as well, but physicists have been slow to accept the invitation.

A two dimensional system of oscillators will synchronize oscillations much more easily than a three dimensional system. Cooper pairs may be understood as being paired exactly antisnchronously, as to their orbit and spin, both of which are quantum oscillations. Quanta are limit cycles.

A particular virtue of this theory--perfectly synchronized oscillations--is that it may explain all types of superconductivity.
not rated yet Oct 22, 2011
Which compounds super-conduct at room temperature?
That is the only question and measure of any SC theory.

Anything else is lip service.
1 / 5 (1) Oct 22, 2011
In dense aether theory the superconductivity is the result of electrons compression within atomic lattice. Electrons can be compressed with their attraction to lines of charge holes, so called the hole stripes, which will form the conductive paths withing material. The only problem is, the electrons are strongly repulsive, so that these hole stripes must be surrounded with many layers of inert atoms, which are exerting a cohesive force. If you want to compress electrons inside of pipe, such a pipe should have a thick walls, literally speaking.

So that the highest temperature superconductor can be made of layers with oxidized atoms in a high oxidation state surrounded with many layers of inert oxides. Such materials enable to reach temperatures of superconductor transition well above 20°C.

1 / 5 (1) Oct 22, 2011
The problem in preparation of room temperature superconductors (RTS) is not in construction of such material, but in their preparation in pure crystalline state. The more oxide layers will separate the superconductive layer of hole stripes, the lower is the probability, the layers of hole stripes will remain continuous across crystal boundaries. We know already, how good superconductor should appear, it's rather geometrical problem of preparation of highly organized superlattices of O=O=O=O=Cu=O=O=O=O=Cu=O=O=O=O type. Such lattices must be made with epitaxial methods layer by layer.
1 / 5 (1) Oct 22, 2011
Before ten years a diamond expert J.F.Prins revealed alternative way to solution of this problem. He injected holes in form of oxygen atoms bellow surface of artificial diamond layers. The electrons are attracted to these holes and they condense at the surface in form of superconductive layer, conducting well above the room temperature.


I do believe, such electrons could be attracted to surface of insulator with external electric charge, too.


So, if we surround well insulated wire with positive charge, the electrons from outside will get attracted to it and they will cover the surface of insulator with superconductive layer of electrons. The only problem is, how to create the sufficiently compact insulator layer, resistant to dielectric breakthrough.