Crystal field studies on the heavy fermion compound CeNi$_8$CuGe$_4$

TL;DR

This study investigates how substituting nickel with copper in CeNi$_{9-x}$Cu$_x$Ge$_4$ affects the crystal field environment and Kondo physics, revealing a quantum phase transition driven by crystal field degeneracy reduction.

Contribution

It provides the first detailed crystal field level scheme for CeNi$_8$CuGe$_4$ using neutron spectroscopy, linking crystal field changes to quantum phase transition mechanisms.

Findings

Observation of two crystal field transitions at 4 K

Crystal field level scheme determined by neutron spectroscopy

Comparison with specific heat measurements confirms the level scheme

Abstract

Substitution of nickel by copper in the heavy fermion system CeNi$_{9-x}$Cu$_x$Ge$_4$ alters the local crystal field environment of the Ce$^{3+}$-ions. This leads to a quantum phase transition near $x\approx0.4$, which is not only driven by the competition between Kondo effect and RKKY interaction, but also by a reduction of an effectively fourfold to a twofold degenerate crystal field ground state. To study the consequences of a changing crystal field in CeNi$_8$CuGe$_4$ on its Kondo properties, inelastic neutron scattering (INS) experiments were performed. Two well-defined crystal field transitions were observed in the energy-loss spectra at 4 K. The crystal field level scheme determined by neutron spectroscopy is compared with results from specific heat measurements.