Persistence of magnetic excitations in La2-xSrxCuO4 from the undoped insulator to the heavily overdoped non-superconducting metal

TL;DR

This study uses RIXS to track magnetic excitations in La2-xSrxCuO4 across the entire phase diagram, revealing persistent magnons even in heavily overdoped, non-superconducting samples, challenging previous assumptions about their role in high-temperature superconductivity.

Contribution

It demonstrates that magnetic excitations persist in heavily overdoped cuprates, suggesting other factors influence the loss of superconductivity beyond magnetic excitation disappearance.

Findings

Magnetic excitations persist up to x=0.40 in La2-xSrxCuO4.

Magnon dispersion remains similar across doping levels.

Superconductivity loss is not due to magnetic excitation disappearance.

Abstract

One of the most intensely studied scenarios of high-temperature superconductivity (HTS) postulates pairing by exchange of magnetic excitations [1]. Indeed, such excitations have been observed up to around optimal doping in the cuprates [2-7]. In the heavily overdoped regime neutron scattering measurements indicate that magnetic excitations have effectively disappeared [8-10], and this was argued to cause the demise of HTS with overdoping [1, 8, 10]. Here we use resonant inelastic x-ray scattering (RIXS), which is sensitive to complementary parts of reciprocal space, to measure the evolution of the magnetic excitations in La2-xSrxCuO4 across the entire phase diagram, from a strongly correlated insulator (x = 0) to a non-superconducting metal (x = 0.40). For x = 0, well-defined magnon excitations are observed [11]. These magnons broaden with doping, but they persist with a similar dispersion and comparable intensity all the way to the non-superconducting, heavily overdoped metallic phase. The destruction of HTS with overdoping is therefore caused neither by the general disappearance nor by the overall softening of magnetic excitations; other factor(s), such as the redistribution of spectral weight, must be considered.