The Dutch physicist Heike Kamerligh Onnes liquefied helium at the turn of the century, achieving a temperature only 4.2 kelvins above absolute zero. He knew that metals' electrical resistance decreased with decreasing temperature and with increasing purity, suggesting the obvious. He cooled a thread of triple-distilled mercury in his liquid helium and discovered the amazing macroscopic quantum mechanical manifestation of superconductivity - a DC electric current forever propagating through a conductor with zero electrical resistance, which won him his Nobel Prize in 1911. Slight magnetic fields quenched the effect, rendering it a laboratory curiosity. These were Type I superconductors.
Type II superconductors were discovered to be quenched only by megagauss magnetic fields, yielding visions of resistance-free giant motors, generators, magnets, power transmission lines and so on. The race was on for a room temperature superconductor! Bardeen, Cooper and Schrieffer won their Nobel for a theory explaining the effect (but not predicting materials exhibiting it). Pairs of negatively charged spin-1/2 electrons (fermions) couple to high frequency lattice vibrations (phonons) to yield integral spin boson constructs which promptly collapse into a degenerate Bose fluid. This boson sea can only be perturbed as a whole. Resistance is an electron-by-electron phenomenon. Direct current flows without resistance, forever or until quenched as a whole. Theory drew a line at about 30 kelvins, above which temperature lattice vibrations were too mushy to support the quantum coupling effect.
(Commonplace MgB2 superconducts at 39 K, but that was discovered in 2001 and nobody can rationalize it to make a second entry.)
Bednorz and Muller, two IBM/Zurich researchers remanded for diverting research funds from their cryogenic insulator project, discovered high temperature ceramic superconductors. Some compositions now push toward dry ice at 195 kelvins (inching toward a Spring day at 293 kelvins) and concurrently evade a decade of intense theoretical scrutiny conducted across the entire planet. While all the sturm and drang of media-hyped research drones on and nobody understands the observations, much less how to control and enhance them, the original proposals for high temperature superconductors languish.
Physicists in the 1960s and 1970s proposed pairing fermion single electrons into bosons by coupling them not with phonons (quantized lattice vibrations) but with excitons (quantized lattice electronic disturbances). The thousandfold lower exciton mass withstands a like temperature increase. A 1000 kelvin superconductor would have its uses. Theory suggested a ladder of dye molecules arrayed upon a rigid polymer backbone. The spatial arrangement, electronic overlap, LUMO/HOMO gap, redox potential, electron affinity gradient... of the molecular dye array could be engineered to fine tune the construct into operability. That such macromolecules could not be built even on paper assured continued funding of theoretical physics without untidy verities of organic synthesis and real world evaluation.
Time's up, folks! We can now build such postulated excitonic superconducting molecules to any specification, perfectly, cheaply and at will. Biological models of stacked planar molecules supported from a high polymer backbone - nucleic acids with their A,T,C,G,U bases and poly(sugar-phosphate) backbones - have been around for 3.5 billion years or more. Both DNA and RNA can be custom synthesized on solid phase polymer supports. Substitute dyes for A,T,C,G,U and Voila! Being chemists, we would first improve upon the natural product in terms of molecular control and persistence, and maybe take a shot at second and third order nonlinear optical phenomena while we are at the bench. Research follows funding. More's the pity.
Biosearch (subsidiary of Millipore Corporation) has commercialized the synthesis of peptide nucleic acids wherein the fragile, reactive and untunable DNA or RNA poly(sugar-phosphate) backbone is supplanted by poly((2-aminoethyl)glycine). Any natural or unnatural trifunctional amino acid or analogue bearing a pair of complimentary sites for controlled stepwise linear polymerization and a third to hook on the borne molecular base or, in our example, dye molecule is satisfactory. The synthesis of polymer chains tens (trivial) or hundreds (merely expensive) of units long is now performed at an hour per segment. We can at will with a modest budget create homopolymers of candidate excitonic dyes with exquisite geometric control and compositional specificity. We can at will and with perfect control create consistent compositional and therefore property gradients along our monomolecular wire to mimic diodes, capacitors, inductors and other useful circuit elements. We even have the bonus of a backbone with one or more asymmetric carbon atoms per segment, inviting non-linear optical effects.
Perhaps dozens of theoretical physics papers published on such dye assemblies were blowing smoke and flashing mirrors, the better to secure tenure or hang in there long enough for emeritus status. Perhaps those guys and gals really knew what they were talking about. Since the relevant experiments are now appropriate to a second year undergraduate genetic engineering lab class, WHAT ARE WE WAITING FOR?
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