Detailed study of the structure of the low-energy magnetic excitations in overdoped La1.75Sr0.25CuO4

To examine the detailed structure of low-energy magnetic excitations in a high-transition-temperature superconducting cuprate with heavily hole-doping, we performed inelastic neutron scattering experiments on La_1.75Sr_0.25CuO₄. We observed clear dispersion relations of the previously reported incommensurate (IC) magnetic correlations at $Q_{\mathrm{tet}}=(0.5\pm \delta ,0.5)/(0.5,0.5\pm \delta )$ [1]. In addition, we show the emergence of continuum magnetic excitations with a ring shape centered at $\Gamma$ point $Q_{\mathrm{tet}}=(0.5,0.5)$ in a constant energy spectrum at $T=50K$. The radius of the ring $(r=0.109)$ is smaller than the incommensurability $(\delta =0.118)$. This suggests that the origin of the ring-like excitations is different from that of the IC magnetic correlations, and the low-energy magnetic excitations of the La_2-xSr_xCuO₄ system are inherently composed of these two kinds of excitations.