title: Multiband superconductivity with unexpected deficiency of nodal quasiparticles in CeCu₂Si₂.
abstract: Superconductivity in the heavy-fermion compound CeCu2Si2 is a prototypical example of Cooper pairs formed by strongly correlated electrons. For more than 30 years, it has been believed to arise from nodal d-wave pairing mediated by a magnetic glue. Here, we report a detailed study of the specific heat and magnetization at low temperatures for a high-quality single crystal. Unexpectedly, the specific-heat measurements exhibit exponential decay with a two-gap feature in its temperature dependence, along with a linear dependence as a function of magnetic field and the absence of oscillations in the field angle, reminiscent of multiband full-gap superconductivity. In addition, we find anomalous behavior at high fields, attributed to a strong Pauli paramagnetic effect. A low quasiparticle density of states at low energies with a multiband Fermi-surface topology would open a new door into electron pairing in CeCu2Si2.
authors.affiliation: Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Shunichiro
authors.initials: S
authors.lastname: Kittaka
authors.affiliation: Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Yuya
authors.initials: Y
authors.lastname: Aoki
authors.affiliation: Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Shimura
authors.affiliation: Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Toshiro
authors.initials: T
authors.lastname: Sakakibara
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
authors.forename: Silvia
authors.initials: S
authors.lastname: Seiro
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Geibel
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Steglich
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ikeda
authors.affiliation: Department of Physics, Okayama University, Okayama 700-8530, Japan.
authors.forename: Kazushige
authors.initials: K
authors.lastname: Machida