Quantum Critical Fluctuations in the Heavy fermion compound Ce(Ni$_{0.935}$Pd$_{0.065}$)$_2$Ge$_2$

TL;DR

This study investigates quantum critical fluctuations in a heavy fermion compound near an antiferromagnetic quantum critical point, revealing non-Fermi liquid behavior and finite spin correlations possibly due to alloy disorder.

Contribution

It provides detailed experimental evidence of quantum critical behavior in Ce(Ni$_{0.935}$Pd$_{0.065}$)$_2$Ge$_2$, highlighting deviations from expected divergence due to disorder effects.

Findings

Resistivity and specific heat follow 3D itinerant AF QCP power laws at low T.

Susceptibility and resistivity show logarithmic and linear T dependence at intermediate T.

Spin correlations remain finite, suggesting disorder influences quantum critical behavior.

Abstract

Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni$_{0.935}$Pd$_{0.065}$)$_2$Ge$_2$ in order to study the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for $T \leq$ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP ($\rho(T) \sim T^{3/2}$ and $\gamma(T) \sim \gamma_0 - b T^{1/2}$). However, for 2 $\leq T \leq$ 10 K, the susceptibility and specific heat vary as $log T$ and the resistivity varies linearly with temperature. Furthermore, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. We suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.