Unpaired electrons in the heavy-fermion superconductor CeCoIn5

Area of Science:

• Condensed matter physics
• Materials science
• Superconductivity

Background:

• Heavy-fermion materials exhibit complex electronic properties.
• Understanding superconductivity in these materials is crucial for technological applications.
• Ce(1-x)La(x)CoIn5 is a model system for studying unconventional superconductivity.

Purpose of the Study:

• To investigate the impact of impurity concentration on the superconducting state of Ce(1-x)La(x)CoIn5.
• To elucidate the coexistence of different electronic states in the superconducting phase.
• To propose a theoretical model explaining the observed phenomena.

Main Methods:

• Measurements of thermal conductivity in the superconducting state.
• Measurements of specific heat in the superconducting state.
• Systematic variation of impurity concentration (x) in Ce(1-x)La(x)CoIn5.

Main Results:

• Suppression of the superconducting transition temperature (T(c)) with increasing impurity concentration.
• Observed increase in residual electronic specific heat, consistent with d-wave superconductivity.
• Contrasting decrease in residual electronic thermal conductivity.
• Evidence for uncondensed electrons coexisting with nodal quasiparticles.

Conclusions:

• The contrasting behaviors of specific heat and thermal conductivity indicate a complex superconducting state.
• A multiband scenario is proposed, featuring a d-wave gap on heavy-electron sheets and a negligible gap on light pockets.
• This study provides insights into the unconventional nature of superconductivity in heavy-fermion compounds.