Evolution of quantum criticality in CeNi(9-x)Cu(x)Ge(4)

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• Heavy fermion systems exhibit complex electronic behaviors driven by localized f-electrons interacting with conduction electrons.
• The interplay between Kondo effect and RKKY interaction governs the ground state properties of cerium-based intermetallics.
• Crystal field splitting influences the degeneracy of the electronic ground state in rare-earth compounds.

Purpose of the Study:

• To investigate the impact of Ni/Cu substitution on the ground state properties of the heavy fermion system CeNi(9-x)Cu(x)Ge(4).
• To explore the quantum critical behavior and its relation to changes in fundamental interactions and ground state degeneracy.

Main Methods:

• Systematic studies of crystal structure, specific heat, thermal expansion, magnetic susceptibility, and electrical resistivity.
• Compositional tuning via Ni/Cu substitution (0≤x≤1) to probe phase transitions.

Main Results:

• A continuous tuning of the ground state was observed with increasing copper content.
• The system transitions from a non-magnetic Kondo ground state in CeNi(9)Ge(4) to a magnetically ordered state in CeNi(8)CuGe(4) with a Néel temperature (T(N)) of 175 ± 5 mK.
• Quantum critical behavior was identified for specific compositions, linked to the Kondo effect, RKKY interaction, and reduced crystal field degeneracy.

Conclusions:

• CeNi(9-x)Cu(x)Ge(4) serves as a unique platform to study substitution-driven quantum phase transitions.
• The observed transition is associated with a delicate balance between Kondo screening, RKKY interactions, and crystal electric field effects.
• This system demonstrates the first instance where a quantum phase transition is linked to a reduction in the effective ground state degeneracy.