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.Comment: 5 pages, 4 figures (main text) + 5 pages, 6 figures (supplemental
material), published in Phys. Rev. Let
