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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. Based on inelastic neutron scattering data, we present the
first in-depth study of the magnetic excitation spectrum in momentum and
energy space in the superconducting and the normal state of CeCu2Si2[1]. A
clear spin excitation gap is observed in the superconducting state.
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. This study represents the first thorough comparison of the competing
energetics for a superconductor near an antiferromagnetic quantum critical
point, as well as for any unconventional low-temperature superconductor.
References: [1] accepted for publication in Nature Physics. in collaboration with O. Stockert, J. Arndt, E. Faulhaber, C. Geibel, H. S. Jeevan, M. Loewenhaupt, K. Schmalzl, W. Schmidt, Q. Si, and F. Steglich |
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