Using Heat to Probe Cool Materials

Gap Structures

Directional heat flow has been used as a probe of the symmetry of a carefully modified barium iron arsenide, superconductor, revealing features that have eluded other experimental methods. Superconductivity occurs because electrons form pairs that are trapped by an energy gap (or gaps) that the electrons cannot occupy. Depending on the direction in which an electron pair is moving, these gaps can be large, small, or even not exist at all. Since electrons carry heat as well as charge, the heat flow carries information about the shape of the superconducting gap along the heat flow direction. Researchers have found that the gap in Ba(Fe1-xCox)As2 is very small for certain directions, and can be made to go to zero by changing the chemical composition, revealing a subtle interplay between the chemistry and physics of these fascinating materials. This result points the way to a more complete understanding of the mechanism of superconductivity in these and other "high temperature" superconductors.

Note: This paper is a Phys. Rev. B Editor's Suggestion and was selected for a Viewpoint in Physics.

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