Two energy scales in the spin excitations of the high-T_c superconductor La$_{2-x}$Sr$_{x}$CuO$_{4}$

TL;DR

This study reveals that collective spin excitations in optimally doped La$_{2-x}$Sr$_{x}$CuO$_{4}$ have a two-component structure with energies matching features seen in electronic spectroscopies, supporting their role in high-temperature superconductivity.

Contribution

The paper demonstrates that collective spin excitations have a structured two-component energy spectrum, aligning with spectroscopic features, thus supporting their significance in superconductivity mechanisms.

Findings

Spin excitations have a two-component structure with energies around 18 meV and 40-70 meV.

The second component carries most spectral weight and matches spectroscopic features.

Collective spin excitations can explain key features in quasiparticle spectroscopies.

Abstract

The excitations responsible for producing high-temperature superconductivity in the cuprates have not been identified. Two promising candidates are collective spin excitations and phonons. A recent argument against spin excitations has been their inability to explain structures seen in electronic spectroscopies such as photoemission and tunnelling. Here we use inelastic neutron scattering to demonstrate that collective spin excitations in optimally doped La$_{2-x}$Sr$_{x}$CuO$_{4}$ are more structured than previously thought. The excitations have a two component structure with a low-frequency component strongest around 18 meV and a broader component strongest near 40-70 meV. The second component carries most of the spectral weight and its energy matches structure seen in photoemission and tunnelling spectra in the range 50-90 meV. Our results demonstrate that collective spin excitations can explain features of quasiparticle spectroscopies and are therefore likely to be the strongest coupled excitations.