European research confirms Babaev’s prediction about superconductivity

Theoretical physicist Egor Babaev recently received welcome confirmation, from experimental work in Belgium and Switzerland, where researchers reported that a distinct new type of non-traditional superconductivity exists, as Babaev predicted as early as 2003 that it would. The laboratory findings help to make up for what he recalls as “quite fierce opposition” his prediction met only a few years ago.

As Babaev explains, the textbook classification of superconducting materials divides them into two classes, type I and type II, depending on their response to an externally applied magnetic field. Type-I superconductivity, discovered first, 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. This type of superconductivity was described in the 1950s by Ginzburg and Landau, work which won a Nobel Prize in 2003. Type II superconductivity was predicted to exist in 1953 by Russian theoretical physicist Alexei Abrikosov, a student of Landau, who said there should be superconducting materials where vortices or “tiny electronic tornadoes,” in Babaev’s words, can form.

Because the vortices are made of circulating electronic flows they carry some magnetic charge and Abrikosov predicted they’d allow an external field to pass through. Abrikosov’s Type II predictions were eventually proved experimentally and he shared the Nobel Prize for this work in 2003. When multiple Abrikosov vortices form in a superconductor they repel each other, spacing themselves evenly apart and forming a pattern called “Abrikosov lattice” in the superconductor that faces the applied field.

The classification scheme of superconductors as Type-I or Type-II turned out to be very robust: All superconducting materials discovered in the last half century can be classified as either, Babaev notes. But working on theories to describe new, complex superconducting materials possessing several kinds of electrons, he eventually predicted that there should be another distinct type that would not fall into either camp. Instead, the new type, he said, would form something like a super-regular Swiss cheese, with clusters of tightly packed vortex droplets bunched together, separated with “voids,” or areas with no vortices and no magnetic field.

More specifically, Babaev predicted that in certain two-component superconducting materials exposed to a magnetic field, there could be a new sort of vortex which would repel others at close distances but (in contrast to Abrikosov vortices) attract each other over longer distances without exhibiting the instability usually associated with attraction. However, to Babaev’s dismay the idea was considered so radical by journal referees he could not publish for some years due to skepticism, much as Abrikosov had experienced in the 1950s.

Babaev recalls that he was “surprised with the quite fierce opposition of some of the referees that an entirely new type of quantum vortex endowed with these exotic properties could exist, even in principle.” His first paper on the subject was never accepted in a peer-reviewed journal but is available as a preprint at www.arxiv.org server. He was able finally to publish this prediction in more detail in Physical Review B in 2005 with Martin Speight.

Then this year, to Babaev’s delight, experiments by Victor Moshchalkov of the Catholic University of Leuven, Belgium with others in Switzerland observed vortex droplets coexisting with voids, consistent with Babaev’s picture of “Meissner domains” in magnesium diboride, a material which for many years was regarded as a regular Type II superconductor.

Furthermore, Moshchalkov’s group extensive analyzed the origin of these voids which led them to the daring proposal that these voids are not a result of defects of the material but are part of its fundamental intrinsic property. This effectively marks the experimental confirmation of a new class of superconductivity Babaev had predicted. Moshchalkov coined the name “Type 1.5 superconductivity” for their discovery.

April 6, 2009.

E-mail story to a friendPrinter-friendly version

/more people/