Filling in Gaps

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Science  11 Feb 2011:
Vol. 331, Issue 6018, pp. 651
DOI: 10.1126/science.331.6018.651-a

Since the discovery of iron-pnictide superconductors 3 years ago, considerable progress has been made in understanding their properties, but the basic mechanism of pairing responsible for superconductivity has yet to be agreed on. The momentum-space structure of the superconducting gap has the potential to shed light on this important question, and one of the most reliable ways to extract it is angle-resolved photoemission spectroscopy (ARPES). So far, ARPES has been used to map the superconducting gap in the momentum plane corresponding to the parallel layers of FeAs in these compounds; now, Xu et al. use variable-energy ARPES to probe the three-dimensional gap function in a representative compound Ba0.6 K0.4Fe2As2. On all five Fermi surfaces, they find a nodeless gap function that disperses in the c-axis direction and is characterized by a single pair of energy scales, one corresponding to intra- and the other to interlayer coupling. Intriguingly, the ratio of these energy scales (the gap anisotropy) is similar to the ratio of magnetic exchange couplings in the corresponding directions, suggesting that antiferromagnetic fluctuations may be driving the pairing in this compound.

Nat. Phys. 7, 10.1038/nphys1879 (2011).

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