Universal Dispersive Excitations in the High-Temperature Superconductors

TL;DR

This study reveals that magnetic excitations in high-temperature superconductors are dispersive, similar across different compounds, and form a continuum at higher energies, indicating complex multi-particle dynamics.

Contribution

It demonstrates universal dispersive magnetic excitations in high-Tc cuprates, linking neutron scattering results across different materials and energy scales.

Findings

Magnetic excitations are dispersive and similar in La$_{2-x}$Sr$_x$CuO$_4$ and YBa$_2$Cu$_3$O$_{6+x}$.

Excitations broaden with energy, forming a continuum at high energies.

Magnetic correlations are two-dimensional, ruling out simple one-dimensional models.

Abstract

High-resolution neutron scattering experiments on optimally doped La$_{2-x}$Sr$_x$CuO$_4$ have been performed which reveal that the magnetic excitations are dispersive. The dispersion is found to be the same as in the YBa$_2$Cu$_3$O$_{6+x}$ family, and is quantitatively related to that observed with charge sensitive probes. The excitations are also found to broaden rapidly with increasing energy, forming a continuum at higher energy, and bear a remarkable resemblance to multi-particle excitations observed in low-dimensional antiferromagnets and some magnetic metals. The magnetic correlations are two dimensional, and so rule out the simplest scenarios where the copper oxide planes are subdivided into weakly interacting one-dimensional magnets.