Persistence of Magnetic Excitations in Overdoped High-Temperature Superconductors
One of the most intensely studied scenarios of high-temperature superconductivity (HTS) postulates pairing by exchange of magnetic excitations. Indeed, such excitations have been observed up to optimal doping in the cuprates. In the heavily overdoped regime, neutron scattering measurements indicate that magnetic excitations have effectively disappeared and this has been argued to cause the demise of HTS with overdoping.
X-ray group scientists Mark Dean, Xuerong Liu and John Hill used used resonant inelastic X-ray scattering (RIXS) to measure the evolution of the magnetic excitations in the HTS Lanthanum Strontium Copper Oxide across the entire doping phase diagram, from a strongly correlated insulator to a non-superconducting metal. At the wavevectors accessible with RIXS, the spin waves or magnon excitations were found to persist with similar energies and intensities even as superconductivity disappears in the heavily doped cuprates.
The fact that magnetic excitations are similar in superconducting and non-superconducting samples restricts theories of superconductivity based on magnetic excitations. One interpretation is that only a particular small subset of the magnetic excitations cause the superconducting pairing.
This work was published online on 04 August 2013 in Nature Materials: M. P. M. Dean, G. Dellea, R. S. Springell, F. Yakhou-Harris, K. Kummer, N. B. Brookes, X. Liu, Y-J. Sun, J. Strle, T. Schmitt, L. Braicovich, G. Ghiringhelli, I. Božović and J. P. Hill, Nature Materials DOI:10.1038/nmat3723.
This work was supported by the U.S. Department of Energy Office of Science.