A Theory That Explains Planar Weight Disparity


26 May 2013
Superconductors.ORG

       Since the discovery of planar weight disparity (PWD) as a Tc enhancement mechanism in 2005, more that 110 new superconductors have been found - 40 of which have Tc's above room temperature.

      However, just as a theory to explain high-temperature superconductivity in the copper-oxides remains elusive, so does an explanation for why alternating the atomic layers heavy-light improves Tc. The effect is so strong that every known HTSC copper-oxide can be shown to exhibit some planar weight disparity along its C axis.

      Now, a theory put forth nearly 20 years ago seems to explain why PWD correlates so strongly with Tc.


       In the mid 1990's Howard Blackstead of Notre Dame and John Dow of A.S.U., postulated that oxygen located in the "chain layer" of a crystal lattice was being compressed into a metallic superconducting state.1

       To quote: "Experimental evidence indicates that the holes of the hypocharged oxygen in the charge-reservoir regions contribute primarily to the superconductivity, contrary to most current models of high- temperature superconductivity, which are based on superconductivity originating in the cuprate-planes. The data suggest that a successful theory of high-temperature superconductivity will be BCS-like and will pair holes through the polarization field, perhaps electronic as well as vibrational polarization."

       Blackstead and Dow's argument is compelling when viewed alongside what has been discovered through the application of planar weight disparity.


       Specifically: Numerous HT superconductors discovered since 2005 have all shown a sudden drop in quiescent noise below Tc, as shown below. Since background noise arises from lattice vibrations, a sharp drop in noise when superconductivity appears is irrefutable evidence that lattice vibrations are intertwined with the superconductivity mechanism.



       Using the simplest structure known to exhibit high-temperature superconductivity, the infinite layer structure (shown above left), we can see the effect lattice vibrations have on oxygen layers. Below left, the compound SrCaCu2O4 which has the highest Tc among the infinite layer superconductors, has been rotated 90 degrees for clarity. (The oxygen atoms are at the corners of each red square.)


         


       The sinusoidal waveforms near the Sr and Ca atoms show the relative frequency of each atom's vibration along the C axis. Since strontium is heavier than calcium, it oscillates at a lower frequency, producing fewer cycles per unit time. The result is that different vibrational frequencies heterodyne at the oxygen layer, producing periodic compression proportional to a complex waveform. However with the Sr2Cu2O4 (non-superconducting) structure to the right, the waveforms cancel at the oxygen layer, due to identical frequencies producing a null heterodyne. Ergo, there absolutely MUST be a difference in mass on opposite sides of the oxygen layer for superconductivity to occur. No periodic compression = no superconductivity.

       When experimentally intermixing various waveform frequencies and amplitudes, the resulting complex waveform increases in amplitude and approaches a more uniform sinusoidal shape as the planar weight ratio increases. And this is exactly what the plots at page top suggest: greater PWD equates to higher Tc due to greater and more periodic (BCS-like) compression of the oxygen layers.



1. Howard A. Blackstead and John D. Dow "Hypercharged copper, hypocharged oxygen, and high-temperature superconductivity", Proc. SPIE 2697, Oxide Superconductor Physics and Nano-Engineering II, 113 (July 5, 1996); doi:10.1117/12.250277; http://dx.doi.org/10.1117/12.250277


E. Joe Eck
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