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Link between spin fluctuations and Cooper pairing in copper oxide superconductors
lthough it is generally accepted that superconductivity (SC) is unconventional in the high transition temperature copper oxides (high-Tc cuprates), the relative importance of phenomena such as spin and charge (stripe) order, SC fluctuations, proximity to a Mott insulator, a pseudogap phase, and quantum criticality are still a matter of great debate. In electron-doped cuprates, the absence of an anomalous pseudogap phase in the underdoped region of the phase diagram and weaker electron correlations, suggest that Mott physics and other unidentified competing orders are less relevant and that antiferromagnetic (AFM) spin fluctuations are the dominant feature. Here we demonstrate that a linear-temperature (T -linear) scattering rate - a key feature of the anomalous normal state properties of the cuprates - is correlated with the Cooper pairing. Through a study of magnetotransport in thin films of the electron-doped cuprate La2-xCexCuO4 (LCCO), we show that an envelope of T-linear scattering surrounds the SC phase, and survives to zero temperature when superconductivity is suppressed by magnetic fields. Comparison with similar behavior found in organic superconductors strongly suggests that the T-linear resistivity is caused by spin-fluctuation scattering. A correlation between T-linear scattering and superconductivity has also been found in hole-doped cuprates.
Therefore, our results suggest a fundamental connection between AFM spin fluctuations and the pairing mechanism of high temperature superconductivity in all cuprates.