Ultrafast dynamics in the presence of antiferromagnetic correlations in electron-doped cuprate La[subscript 2 − x] Ce[subscript x] CuO[subscript 4 ± δ]

Abstract

We used femtosecond optical pump-probe spectroscopy to study the photoinduced change in reflectivity of thin films of the electron-doped cuprate La[subscript 2−x]Ce[subscript x]CuO[subscript 4] (LCCO) with dopings of x=0.08 (underdoped) and x=0.11 (optimally doped). Above T[subscript c], we observe fluence-dependent relaxation rates that begin at a temperature similar to the one where transport measurements first show signatures of antiferromagnetic correlations. Upon suppressing superconductivity with a magnetic field, it is found that the fluence and temperature dependence of relaxation rates are consistent with bimolecular recombination of electrons and holes across a gap (2Δ[subscript AF]) originating from antiferromagnetic correlations which comprise the pseudogap in electron-doped cuprates. This can be used to learn about coupling between electrons and high-energy (ω>2Δ[subscript AF]) excitations in these compounds and set limits on the time scales on which antiferromagnetic correlations are static.