Magnetic fluctuations is the leading candidate for pairing in cuprate, iron-based, and heavy fermion superconductors. This view is challenged by the recent discovery of nodeless superconductivity in CeCu₂Si₂, and calls for a detailed understanding of the corresponding magnetic fluctuations. Here, we mapped out the magnetic excitations in superconducting (S-type) CeCu₂Si₂ using inelastic neutron scattering, finding a strongly asymmetric dispersion for E ≲ 1.5 meV, which at higher energies evolves into broad columnar magnetic excitations that extend to E ≳ 5 meV. While low-energy magnetic excitations exhibit marked three-dimensional characteristics, the high-energy magnetic excitations in CeCu₂Si₂ are almost two-dimensional, reminiscent of paramagnons found in cuprate and iron-based superconductors. By comparing our experimental findings with calculations in the random-phase approximation,we find that the magnetic excitations in CeCu₂Si₂ arise from quasiparticles associated with its heavy electron band, which are also responsible for superconductivity. Our results provide a basis for understanding magnetism and superconductivity in CeCu₂Si₂, and demonstrate the utility of neutron scattering in probing band renormalization in heavy fermion metals.

磁涨落是铜酸盐、铁基和重费米子超导体配对的主要候选者。这一观点受到最近发现的 CeCu ₂ Si ₂无节点超导性的挑战，需要详细了解相应的磁涨落。在这里，我们使用非弹性中子散射绘制了超导（S型）CeCu ₂ Si _{2中的磁激发，发现}E  ≲ 1.5 meV具有强不对称色散 ，在较高能量下演变成宽柱状磁激发，延伸至E  ≳  5兆伏。_{虽然低能磁激发表现出明显的三维特征，但 CeCu 2} Si ₂中的高能磁激发几乎是二维的，让人想起铜酸盐和铁基超导体中发现的顺磁振子。通过将我们的实验结果与随机相位近似中的计算结果进行比较，我们发现CeCu ₂ Si ₂中的磁激发源自与其重电子带相关的准粒子，这些准粒子也负责超导性。_{我们的结果为理解CeCu 2} Si ₂中的磁性和超导性提供了基础，并证明了中子散射在重费米子金属探测带重整化中的实用性。