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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.
