In this work, we used high magnetic fields to strip away the superconductivity so that we could learn more about the nature of the metallic (or resistive) state from which the superconductivity (the zero-resistive state) emerges. Whatever scatters the electrons in the metallic state, thus causing it to become resistive, may also be the same interaction that causes the electrons to form the superconducting state. Thus, it is believed that studying the nature of the underlying metallic state can provide important clues as to the origin of the superconductivity - always the holy grail in this area of research.

Many researchers in the field think that superconductivity in the two families of high-temperature superconductors share a common origin - the vibrations (or fluctuations) of the spins on the copper or iron atoms within the crystalline lattice. Theory argues that superconductivity is optimised when these fluctuations become "critical", ie when the ordering of these spins occurs at zero Kelvin - the absolute zero of our temperature scale. This article lends strong support to this idea for the iron-based pnictides, first shown most clearly by Professor Tony Carrington in a Science paper published in 2012. The nature of the underlying resistive state in the copper-based superconductors was revealed by Professor Nigel Hussey's group in an earlier paper, also published in Science, back in 2009. The striking differences now revealed between the two families now casts doubt on whether the same theoretical arguments can be applied to the copper-based superconductors, whose superconducting transition temperatures are about twice as high. For them, a fundamentally new theory may be required.

See http://www.nature.com/nphys/journal/vaop/ncurrent/abs/nphys2869.html to read more.