Superconducting through dense barriers

The jolt of excitement from the January discovery of a new high-temperature superconducting metal, magnesium diboride (MgB2) may get another boost with evidence that the material can carry electrical currents at high density.

The jolt of excitement from the January discovery of a new high-temperature superconducting metal, magnesium diboride (MgB2) may get another voltage boost with evidence that the material can carry electrical currents at high density.

A team of scientists from the Applied Superconductivity Centre at the University of Wisconsin-Madison discovered that the material carries large currents without the common barriers seen in the ceramic superconductors in development for electric power applications.

High current densities are said to be vital for enabling superconductivity to enter the mainstream electric utility industry, breaking out from existing medical and scientific uses.

The research team found that MgB2 is capable of transporting high electrical currents, because, unlike the ceramic superconductors, the grain boundaries between crystals do not obstruct current flow.

The discovery by Japanese scientists that MgB2 superconducts up to 39 degrees Kelvin (-390 degrees Fahrenheit), almost twice the temperature of any other metallic superconductor, could be a major step toward moving superconductivity from limited application to everyday use.

Superconducting materials have the ability to conduct electricity with almost no loss of energy, and are currently being tested in large demonstration motors and power cables to bring high efficiency to energy transmission.

But the essential challenge for applications of superconductivity is not just to work at higher temperatures, but to fabricate wires that carry high densities of electric current, said David Larbalestier, principal author and ASC director. Current has to manoeuvre through billions of obstructive grain boundaries in the ceramic superconductors.

Because of the obstructive effects of such crystal boundaries, today’s ceramic superconductors reach only about one-fourth to one-tenth of their potential to carry electricity across distances, said Larbalestier.

What the research team found with MgB2 was that crystal boundaries did not obstruct current, allowing high current densities to flow unimpeded. And this compound is unlikely to be the only simple metal boride that superconducts. ‘Sister compounds that work to higher temperatures than MgB2 probably exist and are under intense study,’ he concluded.