Disappearance of antiferromagnetic spin excitations in over-doped La$_{2-x}$Sr$_{x}$CuO$_{4}$

TL;DR

This study investigates how magnetic excitations in over-doped La$_{2-x}$Sr$_{x}$CuO$_{4}$ diminish with increased doping, revealing that magnetism likely originates from fluctuating antiferromagnetic regions rather than Fermi surface nesting.

Contribution

It provides experimental evidence that magnetic excitations decrease with over-doping, suggesting a shift in the magnetic origin from Fermi surface effects to localized antiferromagnetic regions.

Findings

Magnetic excitations decrease with over-doping.

Magnetism is not related to Fermi surface nesting.

Antiferromagnetic regions likely diminish with doping.

Abstract

Magnetic excitations in the energy range up to 100 meV are studied for over-doped La$_{2-x}$Sr$_{x}$CuO$_{4}$ with $x=0.25$ and 0.30, using time-of-flight neutron spectroscopy. Comparison of spectra integrated over the width of an antiferromagnetic Brillouin zone demonstrates that the magnetic scattering at intermediate energies, $20 \lesssim \omega \lesssim 100$ meV, progressively decreases with over-doping. This strongly suggests that the magnetism is not related to Fermi surface nesting, but rather is associated with a decreasing volume fraction of (probably fluctuating) antiferromagnetic bubbles.