Ultrafast dynamics in the presence of antiferromagnetic correlations in electron-doped cuprate La$_{2-x}$Ce$_x$CuO$_{4\pm\delta}$

TL;DR

This study uses femtosecond spectroscopy to investigate how antiferromagnetic correlations influence ultrafast electron dynamics in electron-doped cuprates, revealing bimolecular recombination processes related to the pseudogap.

Contribution

It provides new insights into the ultrafast dynamics associated with antiferromagnetic correlations and the pseudogap in electron-doped cuprates using pump-probe spectroscopy.

Findings

Relaxation rates depend on fluence and temperature, correlating with antiferromagnetic signatures.

Recombination across an antiferromagnetic gap explains observed relaxation behavior.

Results set limits on the timescales of static antiferromagnetic correlations.

Abstract

We used femtosecond optical pump-probe spectroscopy to study the photoinduced change in reflectivity of thin films of the electron-doped cuprate La$_{2-x}$Ce$_x$CuO$_4$ (LCCO) with dopings of x$=$0.08 (underdoped) and x$=$0.11 (optimally doped). Above T$_c$, we observe fluence-dependent relaxation rates which onset at a similar temperature that transport measurements first see signatures of antiferromagnetic correlations. Upon suppressing superconductivity with a magnetic field, it is found that the fluence and temperature dependence of relaxation rates is consistent with bimolecular recombination of electrons and holes across a gap (2$\Delta_{AF}$) originating from antiferromagnetic correlations which comprise the pseudogap in electron-doped cuprates. This can be used to learn about coupling between electrons and high-energy ($\omega>2\Delta_{AF}$) excitations in these compounds and set limits on the timescales on which antiferromagnetic correlations are static.