Reconciling SuperExchange with Planar Weight Disparity

        Recently the JC Davis Group claimed to have confirmed the electron-coupling mechanism that facilitates high temperature superconductivity (HTSC) in the copper-oxides^[1]. They assert that antiferromagnetic spin–spin interactions of electrons, in a process called “superexchange”, are the glue behind Cooper-pairing. Antiferromagnetism is a form of magnetic ordering where electrons align in a regular pattern of neighboring spins rotating in opposite directions. Although the net magnetic field is zero, such a material does have a microscopic magnetic moment at the quantum level (shown above). And with magnetization comes inductance. (Hold that thought.)

        In 2013 Superconductors.ORG (SCO) discovered that there absolutely had to be a difference in the atomic weight of atoms positioned on opposite sides of oxygen within a crystal lattice for that material to become superconductive. This arrangement was dubbed "planar-weight-disparity"(PWD). Oscillations in the above Sr-O-Ca-O example are powered by lattice vibrations - the same thermal energy that causes resistance to appear in a normal conductor. Since heavy atoms vibrate slower than light atoms, PWD results in heterodyne compression of the interposed oxygen atoms along the C axis. The oxygen then responds laterally along the A-B axis to affect the interatomic CuO2 "gap". This is the critical timing mechanism that administrates thermal energy within a superconductor. Without periodic compression (modulation) of the oxygen atoms in HTSC cuprates, superconductivity could not be established.

       Then in 2014 further research by SCO found a direct correlation between the relative permittivity (dielectric constant) of sub-structures within the superconductor lattice and transition temperature (Tc) (see graphic above). This means that electrostatic charges are at work in the electron-pairing process. And with electrostatic charges comes capacitance. When both inductance and capacitance are powered by thermal energy, a superconductor becomes a resonating electronic circuit. To illustrate this an equivalent electronic schematic has been placed beside an infinite layer structure at page top. Each component's function is noted and the arrow in the middle indicates a variable flow of electrons in sync with the PWD periodic compression rate.

       As part of their pairing mechanism discovery the Davis Group also observed changes in the charge transfer gap (CTG) between the copper and oxygen atoms. As the gap narrowed they found the exchange of electrons increased. So, how would PWD affect the charge transfer gap? Jeff Tallon, a recognized authority in the field of superconductivity at Victoria University in New Zealand, speculated: "I would imagine that planar weight disparity would lead to an alternating modulation of the CTG – something like what Seamus Davis showed in his STM measurements. So a modulation rather than an overall shift."(see graphic above right)



       So, does this "modulation" of the charge transfer gap by planar weight disparity affect bulk superconductivity? BSCCO's 2212 structure is actually much larger than the infinite layer structure used as an example earlier in this page. The above graphic shows more oxygen atoms are being compressed. Sr is in opposition to both Ca and Bi. So, if anything, the effect of PWD should be more pronounced. To quote the Davis Group's article in PNAS: "X-ray scattering studies of the Bi2Sr2CaCu2O8+x crystal supermodulation demonstrate that ... the displacement amplitude of the C axis supermodulation is greater in the CuO2 layer than in the adjacent SrO layer." This confirms that while superexchange is facilitating superconductivity in BSCCO, PWD is modulating the CuO2 layers and providing an electronic resonance assist. Superexchange and PWD appear to be two sides of the same coin. To read more about superconductivity and resonant electronic circuits click here.

E. Joe Eck
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1. Shane M. O’Mahony, Wangping Ren, Weijiong Chen, Yi Xue Chong, Xiaolong Liu, H. Eisaki, S. Uchida, M. H. Hamidian, and J. C. Séamus Davis

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