Hourglass magnetic spectrum in charge-stripe-ordered cobalt oxide

Peter Babkevich (EPFL)

A universal, hourglass-shaped magnetic spectrum as measured by inelastic neutron scattering has been found in a number of hole-hoped copper oxide superconductors. This form of a spectrum emerges naturally from a stripe-ordered ground state which led some theoreticians to believe that stripe fluctuations may be an important mechanism of superconductivity. However, the origin of the hourglass in copper-oxide materials has been widely contested.

Instead, we have focused our efforts on an insulating, layered cobalt oxide La_2-xSr_xCoO₄. Our findings in 2011 showed that it too has a characteristic hourglass-like magnetic spectrum. However, direct evidence for a stripe-ordered ground state has been missing and that has led some studies to propose an alternative stripe-free scenario. I will present the results of our polarised neutron diffraction experiments to examine the magnetic order in La_2-xSr_xCoO₄ and discuss its implications on the role of stripes in forming an hourglass spectrum.