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

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${}_{6+\ensuremath{\delta}}$ (superconducting ${T}_{c}=6$ K), a model compound whose normal-state charge transport and thermodynamic properties have been shown to exhibit canonical Fermi-liquid behavior. Complementary RIXS experiments on slightly overdoped Tl${}_{2}$Ba${}_{2}$CuO${}_{6+\ensuremath{\delta}}$ (${T}_{c}=89$ K) and on Y${}_{1\ensuremath{-}x}$Ca${}_{x}$Ba${}_{2}$Cu${}_{3}$O${}_{6+\ensuremath{\delta}}$ 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, indicating the persistence of substantial antiferromagnetic spin correlations over a wide doping range. The surprising coexistence of such correlations with Fermi-liquid-like charge excitations in highly overdoped cuprates poses a challenge to current theoretical models of correlated-electron metals.