Magnetically driven superconductivity in CeCu2Si2

TL;DR

This study uses inelastic neutron scattering to reveal a spin excitation gap and magnetic energy changes in CeCu2Si2, supporting antiferromagnetic fluctuations as the pairing mechanism in heavy-fermion superconductivity.

Contribution

First detailed momentum-energy spectrum analysis of CeCu2Si2 revealing magnetic excitations' role in superconductivity.

Findings

Observation of a spin excitation gap in the superconducting state

Magnetic exchange energy decreases more than the condensation energy

Antiferromagnetic excitations drive Cooper pairing

Abstract

The origin of unconventional superconductivity, including high-temperature and heavy-fermion superconductivity, is still a matter of controversy. Spin excitations instead of phonons are thought to be responsible for the formation of Cooper pairs. Using inelastic neutron scattering, we present the first in-depth study of the magnetic excitation spectrum in momentum and energy space in the superconducting and the normal states of CeCu2Si2. A clear spin excitation gap is observed in the superconducting state. We determine a lowering of the magnetic exchange energy in the superconducting state, in an amount considerably larger than the superconducting condensation energy. Our findings identify the antiferromagnetic excitations as the major driving force for superconducting pairing in this prototypical heavy-fermion compound located near an antiferromagnetic quantum critical point.