Multiband superconductivity with unexpected deficiency of nodal quasiparticles in CeCu2Si2

TL;DR

This study reveals multiband full-gap superconductivity in CeCu2Si2, challenging the traditional nodal d-wave pairing model, through specific heat and magnetization measurements indicating unexpected exponential decay and multiband features.

Contribution

It provides the first evidence of multiband full-gap superconductivity in CeCu2Si2, contradicting the long-held belief of nodal d-wave pairing in this compound.

Findings

Exponential decay in specific heat suggests full-gap superconductivity.

Absence of field-angle oscillations indicates multiband behavior.

Anomalous high-field behavior linked to Pauli paramagnetic effects.

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.