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TT: Fachverband Tiefe Temperaturen

TT 56: CE: Heavy Fermions

TT 56.7: Talk

Thursday, March 17, 2011, 18:15–18:30, HSZ 105

Magnetically driven superconductivity in CeCu₂Si₂ — •S. Kirchner^1,2, O. Stockert², J. Arndt², E. Faulhaber^3,4, C. Geibel², H.S. Jeevan², M. Loewenhaupt⁴, K. Schmalzl⁵, W. Schmidt⁵, Q. Si⁶, and F. Steglich² — ¹Max-Planck-Institut PKS, Dresden, Germany — ²Max-Planck-Institut CPfS, Dresden, Germany — ³Institut für Festkörperphysik, TU Dresden, Dresden, Germany — ⁴Gemeinsame Forschergruppe Helmholtz-Zentrum Berlin – TU Dresden, Garching, Germany — ⁵Forschungszentrum Jülich, Jülich Centre for Neutron Science at Institut Laue-Langevin, Grenoble, France — ⁶Dept. of Physics and Astronomy, Rice Univ., Houston, USA

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. [1] accepted for publication in Nature Physics.