A New Kind of Superconductivity
October 25, 2011 Leave a comment
This month, a group of physicists have published three papers revising the theory of superconductivity. Superconductivity is a phenomenon where a material conducts electricity with no electrical resistance, and also (in some cases) expels magnetic fields within it. It was discovered 100 years ago, in 1911, and since then it’s been refined and applied, for example in the creation of MRI machines and particle accelerators (like the LHC at CERN). The use of superconductivity is limited because it only occurs at very low temperatures, but advancements in physics have raised that temperature threshold considerably, and presumably superconductivity will be more and more important in future technology.
Since I know next to nothing about superconductivity, a theoretical breakthrough in that field means very little to me, but it does offer a good opportunity for us to get an overview of the theory. We’ll be ready for the next theoretical superconductivity news!
For years, most physicists believed that superconductors must be either Type I or Type II. Type 1.5 superconductivity is the subject of intense debate because until now there was no theory to connect the physics with micro-scale properties of real materials, say Egor Babaev of UMass Amherst, currently a fellow at the technology institute in Stockholm, with Mikhail Silaev, a postdoctoral researcher there.
Their new papers now provide a theoretical framework to allow scientists to calculate conditions necessary for the appearance of Type 1.5 superconductivity, which exhibits characteristics of Types I and II previously thought to be antagonistic.
Superconductivity is a state where electric charge flows without resistance. In Type I and Type II, charge flow patterns are dramatically different. Type I, discovered in 1911, has two state-defining properties: Lack of electric resistance and the fact that it does not allow an external magnetic field to pass through it. When a magnetic field is applied to these materials, superconducting electrons produce a strong current on the surface which in turn produces a magnetic field in the opposite direction. Inside this type of superconductor, the external magnetic field and the field created by the surface flow of electrons add up to zero. That is, they cancel each other out.
Type II superconductivity was predicted to exist by a Russian theoretical physicist who said there should be superconducting materials where a complicated flow of superconducting electrons can happen deep in the interior. In Type II material, a magnetic field can gradually penetrate, carried by vortices like tiny electronic tornadoes, Babaev explains. The combined works that theoretically described Type I and II superconductivity won the Nobel Prize in 2003.
Classifying superconductors in this way turned out to be very robust: All superconducting materials discovered in the last half-century can be classified as either, Babaev says. But he believed a state must exist that does not fall into either camp: Type 1.5. By working out the theoretical bases for superconducting materials, he had predicted that in some materials, superconducting electrons could be classed as two competing types or subpopulations, one behaving like electrons in Type I material, the other behaving like electrons in a Type II material.
Babaev also said that Type 1.5 superconductors should form something like a super-regular Swiss cheese, with clusters of tightly packed vortex droplets of two kinds of electron: one type bunched together and a second type flowing on the surface of vortex clusters in a way similar to how electrons flow on the exterior of Type I superconductors. These vortex clusters are separated by “voids,” with no vortices, no currents and no magnetic field.
A more basic introduction to superconductivity can be found in somewhat-overlapping articles at HowStuffWorks and CERN. The punchline in both articles is “The future of superconductivity research is to find materials that can become superconductors at room temperature. Once this happens, the whole world of electronics, power and transportation will be revolutionized.” Transmitting electricity through wires without losing any energy to heat will be a huge boost to energy efficiency, and mastering magnetic repulsion would enable widespread use of fast, cheap Maglev trains (trains that hover over tracks and are propelled using magnetic repulsion).
You’ll certainly be hearing more about superconductivity breakthroughs in the not-so-distant future.