Robustness of magnons near the quantum critical point in the heavy-fermion superconductor CeCu2Si2

Abstract

Paramagnons are supposed to provide the pairing glue for unconventional superconductors. For the heavy-fermion superconductor ${\mathrm{CeCu}}_{2}{\mathrm{Si}}_{2}$, there is indeed good evidence from inelastic neutron scattering (INS) that spin fluctuations drive the superconductivity. Here, we present the INS measurement of the inelastic response of the antiferromagnetic parent compound, `A-type' ${\mathrm{CeCu}}_{2}{\mathrm{Si}}_{2}$, to probe the relation to the excitations of the superconducting (`S-type') sample. We find that the dispersion is very similar in the antiferromagnetic state and in the normal state of the superconducting sample. Pronounced differences to the response in the superconducting state exist at low energies around the zone center. These findings are in line with observations of other unconventional superconductors.