Looking for superconductivity in an hour-glass

25 March 2011

Oxford researchers Peter Babkevich, D. Prabhakaran and Andrew Boothroyd, together with Paul Freeman from Berlin, have uncovered new evidence that dynamic stripe fluctuations play an important role in the copper oxide high temperature superconductors. Their results, which appeared in Nature magazine on 17 March, will assist the search for a mechanism of high temperature superconductivity.

New evidence suggests fluctuating magnetic stripes are the cause of a mysterious hour-glass feature in the magnetic spectrum of high temperature superconductors

One of the intriguing features of the copper oxide high temperature superconductors, discovered in 1986 by Bednorz and Mueller, is the existence of stripe-like patterns of spin and charge found on the planes of copper and oxygen atoms from which the crystal structure is built. Evidence has gradually accumulated over the past 15 years that the motions of these stripes may play a role in the formation of superconductivity, but efforts to probe their dynamical properties experimentally have been hampered by the weakness of the signal and by complications due to superconductivity.

The team from Oxford and Berlin studied a cobalt oxide compound from outside the family of the copper oxide superconductors but with a similar stripe-like magnetic pattern. They used neutron scattering facilities at the Institut Laue-Langevin in Grenoble, France (www.ill.eu), to probe the correlated motions of the atomic magnetic moments. The experiment revealed a magnetic spectrum which has the same appearance – in the shape of an hour-glass – as found universally in the copper oxide superconductors, providing strong evidence that fluctuating magnetic stripes cause the hour-glass spectrum in the copper oxide superconductors. The results suggest that magnetic stripes are a key ingredient in the function of the copper-oxide superconductors.

Oxford team members: Mr Peter Babkevich, Dr D. Prabhakaran and Prof Andrew Boothroyd.