Evidence for spin-fluctuation-mediated superconductivity in electron-doped cuprates

In conventional, phonon-mediated superconductors, the transition temperature and the linear-in-temperature normal-state scattering rate are linked through the electron–phonon coupling strength. In cuprate high-temperature superconductors, no equivalent relationship between critical temperature and electron–boson coupling has been identified. Here we highlight such a link with electrons scattering off commensurate antiferromagnetic spin fluctuations of variable strength. We use d.c. resistivity and high-field magnetoresistance to extract the scattering rate in electron-doped La 2− x Ce x CuO 4 as a function of doping. We reveal a highly anisotropic inelastic component to the scattering rate whose magnitude diminishes markedly as doping increases. The correlation we highlight between the strength of scattering and the critical temperature then identifies low-energy spin fluctuations as the primary pairing glue in electron-doped cuprates. The contrasting magnetotransport behaviour in hole-doped cuprates suggests that the higher critical temperature in those materials cannot be attributed solely to an increase in the coupling strength to the antiferromagnetic fluctuations. The success in modelling La 2− x Ce x CuO 4 reinforces the notion that resolving the origin of high-temperature superconductivity in hole-doped cuprates may require more than a simple extension of the Bardeen–Cooper–Schrieffer theory.