Superconductivity is a state of matter reached by some materials when they are cooled to very low temperatures. It is one of the most fascinating phenomena known to Humankind, enabling materials to conduct electricity without any resistance and to levitate in a magnetic field.
In addition to its technological applications, superconductivity is also an essential playground for physicists – for example, the theory predicting the Higgs boson is based on broken-symmetry ideas from superconductivity.
At the heart of superconductivity is Cooper pairing, a phenomenon in which electrons circumvent their mutual repulsion to form pairs.
A paper to appear in Physical Review Letters presents experimental and theoretical evidence that in two materials containing Nickel, Lanthanum and Carbon or Gallium, LaNiC2 and LaNiGa2, the structure of the Cooper pairs is highly unusual: electrons whose intrinsic magnetisations point in different directions participate differently in the pairing.
This phenomenon has only been encountered before in materials whose non-superconducting state is already magnetic. The authors argue that a hitherto overlooked coupling between magnetism and superconductivity is behind this, suggesting that a re-examination of the relation between these two important phenomena may be necessary.
A. D. Hillier, J. Quintanilla, B. Mazidian, J. F. Annett, R. Cywinski
Research date: August 2012
Contact: Dr Adrian Hillier
Further reading: A. D. Hillier, J. Quintanilla, B. Mazidian, J. F. Annett, R. Cywinski, Phys. Rev. Lett. 109, 097001 (2012).