Identifying high-temperature superconductors

An advance in developing new high-temperature superconducting materials – which could be used in lossless electrical grids, next-generation supercomputers and levitating trains – has been made by researchers from the University of Cambridge, writes Richard Wilson.

Map of superconducting copper oxide structure. Credit: Nicolle R Fuller

Map of superconducting copper oxide structure. Credit: Nicolle R Fuller

They have found that ripples of electrons, known as charge density waves or charge order, create twisted ‘pockets’ of electrons in these materials, from which superconductivity emerges.

Key to conventional superconductors are the interactions of electrons with the lattice structure of the material. These interactions generate a type of ‘glue’ which holds the electrons together.

The strength of the glue is directly related to the strength of the superconductor, and when the superconductor is exposed to an increase in temperature or magnetic field strength, the glue is weakened, the electron pairs break apart and superconductivity is lost.

“We’re trying to understand what sorts of interactions were happening in the material before the electrons paired up, because one of those interactions must be responsible for creating the glue,” said Dr Sebastian.

“Once the electrons are already paired up, it’s hard to know what made them pair up. But if we can break the pairs apart, then we can see what the electrons are doing and hopefully understand where the superconductivity came from.”

Superconductivity tends to override other properties. For example, if in its normal state a superconductor was a magnet, suppressing that magnetism has been found to result in superconductivity.

“So by determining the normal state of a superconductor, it would make the process of identifying new ones much less random, as we’d know what sorts of materials to be looking for in the first place,” said Dr Sebastian.

Previous attempts to determine the origins of superconductivity by determining the normal state have used temperature instead of magnetic field to break the electron pairs apart, which has led to inconclusive results.

“By identifying other materials which have similar properties, hopefully it will help us find new superconductors at higher and higher temperatures, even perhaps materials which are superconductors at room temperature, which would open up a huge range of applications,” said Dr Sebastian.

See the June 15th issue of the journal Nature.

See Cambridge team identifies high-temperature superconductors


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