A Theory of High-temperature Superconductivity

Scientists at Brookhaven National Laboratory have a potential  explanation for high-temperature superconductivity of cuprates, the superconducting breakthrough of the 1980s. They theorize that a certain density of electron pairs is required and when the density is too small or too great, superconductivity disappears.

They painstakingly created many different cuprates with different amounts of doping to create cuprates (actually, 2500 different compounds of lanthanum, strontium copper and oxygen) with differing number of electron pairs using an amazing beam epitaxy system to create each compound layer by layer. Because cuprates have 50 atoms per unit cell, it’s very easy to get a mixture of compounds, so it’s hard to know what kind of result you are seeing. They fixed that problem with this:

This beam epitaxy system builds compounds layer by layer and has some awesome built-in surface chemistry tools, like an absorption spectrometer and an electron diffraction gizmo to monitor surface morphology, thickness, chemical composition, and crystal structure of the resulting thin films in real time.

This is exceptionally elegant work, and points to potential understanding of  a general theory which may help in finding room-temperature superconductors.

Homework: Dependence of the critical temperature in overdoped copper oxides on superfluid density , I. Božović, X. He, J. Wu & A. T. Bollinger