CeCu2Si2

CeCu2Si2 is a cerium-based intermetallic compound that stands as a prototype heavy-fermion system and a landmark in the study of unconventional superconductivity. It crystallizes in the tetragonal ThCr2Si2-type structure, with layers formed by cerium and transition metal-silicon networks. Its electronic behavior is dominated by strong correlations among Ce 4f electrons and conduction electrons, giving rise to a Kondo lattice and large effective electron masses.

The material was discovered to superconduct at very low temperatures by Steglich and coworkers in 1979, with a transition temperature around 0.6 K at ambient pressure. CeCu2Si2 also exhibits magnetic order in some samples, reflecting its proximity to a magnetic quantum critical point. Application of pressure can modify the ground state, often enhancing superconductivity and, in some cases, leading to coexistence or competition between antiferromagnetism and superconductivity. Reported Tc values under pressure span roughly from about 1 K to near 2 K, depending on sample quality and composition.

The superconductivity in CeCu2Si2 is considered unconventional, likely mediated by magnetic (spin) fluctuations rather than phonons. Indications of line nodes in the superconducting gap point to non-s-wave pairing, though the exact order parameter symmetry remains a topic of investigation. The compound is highly sensitive to stoichiometry and sample preparation; small changes can shift the balance between magnetism and superconductivity.

CeCu2Si2 is a foundational system in heavy-fermion physics and quantum criticality, providing key insights into the interplay between magnetism and unconventional superconductivity. It has spurred extensive study of related Ce-based materials and remains a benchmark for theories of strongly correlated electron systems.