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 \ys{superconducting (S-type)} CeCu2Si2 using inelastic neutron scattering, finding a strongly asymmetric dispersion for E≲1.5~meV, which at higher energies evolve 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.
@article{arxiv.2105.00387,
title = {High-energy magnetic excitations from heavy quasiparticles in CeCu$_2$Si$_2$},
author = {Yu Song and Weiyi Wang and Chongde Cao and Zahra Yamani and Yuanji Xu and Yutao Sheng and Wolfgang Löser and Yiming Qiu and Yi-feng Yang and Robert J. Birgeneau and Pengcheng Dai},
journal= {arXiv preprint arXiv:2105.00387},
year = {2021}
}