Dispersive spin excitations in highly overdoped cuprates revealed by resonant inelastic x-ray scattering

TL;DR

This study uses resonant inelastic x-ray scattering to reveal dispersive spin excitations in highly overdoped cuprates, showing a coexistence of Fermi-liquid behavior and high-energy spin excitations similar to undoped antiferromagnetic insulators.

Contribution

It provides new experimental evidence of high-energy spin excitations in highly overdoped cuprates, challenging existing theoretical models.

Findings

Dispersive spin excitations observed in overdoped Tl$_2$Ba$_2$CuO$_{6+eta}$

Spin excitation energies similar to undoped cuprates

Coexistence of Fermi-liquid behavior and high-energy spin excitations

Abstract

Using resonant inelastic x-ray scattering (RIXS) at the Cu $L$-absorption edge, we have observed intense, dispersive spin excitations in highly overdoped Tl$_2$Ba$_2$CuO$_{6+\delta}$ (superconducting $T_c =6$ K), a compound whose normal-state charge transport and thermodynamic properties have been studied extensively and shown to exhibit canonical Fermi-liquid behavior. Complementary RIXS experiments on slightly overdoped Tl$_2$Ba$_2$CuO$_{6+\delta}$ ($T_c =89$ K) and on Y$_{1-x}$Ca$_{x}$Ba$_2$Cu$_3$O$_{6+\delta}$ compounds spanning a wide range of doping levels indicate that these excitations exhibit energies and energy-integrated spectral weights closely similar to those of antiferromagnetic magnons in undoped cuprates. The surprising coexistence of Fermi-liquid-like charge excitations and high-energy spin excitations reminiscent of antiferromagnetic insulators in highly overdoped compounds poses a challenge to current theoretical models of the cuprates.