Feedback spin resonance in superconducting CeCu2Si2 and CeCoIn5

Area of Science:

• Condensed Matter Physics
• Superconductivity Research
• Materials Science

Background:

• Heavy-fermion superconductors like CeCoIn5 and CeCu2Si2 exhibit complex electronic behaviors.
• Spin resonance modes have been observed in these materials, but their origin and relation to superconductivity were unclear.

Purpose of the Study:

• To identify the nature of spin resonance modes in heavy-fermion superconductors.
• To determine the superconducting gap symmetry in CeCoIn5 and CeCu2Si2.
• To establish a criterion for gap symmetry and node positions using magnetic excitation analysis.

Main Methods:

• Analysis of superconducting feedback on magnetic excitations.
• Theoretical modeling of spin resonance modes as magnetic excitons.
• Investigating the wave vector (Q) dependence of resonance states.

Main Results:

• Spin resonance modes in CeCoIn5 and CeCu2Si2 originate from superconducting quasiparticles, identified as magnetic excitons.
• The superconducting gap symmetry in both compounds is determined to be a singlet d_{x;{2}-y;{2}} state.
• This resolves the ambiguity in gap symmetry for CeCoIn5 and provides a similar explanation for resonance peaks as in cuprates.

Conclusions:

• The study reveals a unified origin for spin resonance peaks in heavy-fermion superconductors and cuprates.
• The findings provide a powerful experimental criterion for determining unconventional superconducting gap symmetry.
• The d_{x;{2}-y;{2}} singlet state symmetry is confirmed for CeCoIn5 and CeCu2Si2.