Figure 1: Crystal structure of the new material determined using GEM data and the superconducting order parameter measured using MuSR.
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Since the discovery in 2008 of superconducting materials based on iron there has been intense research into how their superconducting critical temperature can be increased. A team led by Simon Clarke and Stephen Blundell from Oxford University developed a new approach to increase the critical temperature for superconductivity.
The use of the neutron and muon facilities at ISIS was key to characterising the structure by enabling the light atoms to be located and for measurement of some of the fundamental superconducting properties such as the penetration depth.
Simon Clarke said: "Our new results are the first characterisation of an example in which a molecular species has been incorporated into the structure of such a material. Excitingly, we have discovered that in this case this leads to superconductivity up to 43 kelvin, higher than in any iron selenide-derived compound reported so far." Before the molecules are inserted iron selenide only superconducts at up to 8 kelvin.
ISIS neutrons were used to determine the crystal structure of the new material. They are particularly sensitive to the position of the hydrogen atoms within the structure and the difference in how neutrons scatter from hydrogen and deuterium was used to determine how the molecules were incorporated between the superconducting layers.
ISIS muons were used to show that this material is a superconductor that behaves similarly to normal iron selenide, but with features occurring at five times higher temperatures. They also provided information to show how the molecules act as spacers rather than taking part in the superconductivity themselves.
It is hoped that the huge variety of molecules similar to those studied here can be intercalated into this and other related layered superconductors to both increase the critical temperature and perhaps even lead to new sorts of functional materials.
Instruments used: GEM, HRPD, and MuSR.
Matthew Burrard-Lucas et al.
Research date: March 2012
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