Anomalous scaling behavior of the dynamical spin susceptibility of Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$

TL;DR

This study investigates the scaling behavior of dynamical spin susceptibility in a heavy fermion compound near a quantum critical point, revealing unconventional temperature independence and a unique high-temperature scaling form.

Contribution

It provides new insights into the anomalous scaling behavior of spin fluctuations, challenging existing quantum critical theories in heavy fermion systems.

Findings

Spin susceptibility saturates at low temperatures, contrary to divergence expectations.

A unique high-temperature scaling form with sublinear temperature exponent is observed.

Scaling behavior varies with wavevector and occurs above a certain temperature threshold.

Abstract

Inelastic neutron scattering measurements have been performed on single crystals of the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$ in broad energy [0.1, 9.5 meV] and temperature [40 mK, 294 K] ranges in order to address the question of scaling behavior of the dynamical spin susceptibility at the quantum critical point of an itinerant magnetic system. For two wavevectors $\mathbf{Q}$ corresponding to uncorrelated and antiferromagnetically correlated spin fluctuations, it is found that the dynamical spin susceptibility $\chi''(\mathbf{Q},E,T)$ is independent of temperature below a cut-off temperature $T_{\mathbf{Q}}$: the spin fluctuation amplitude saturates at low temperatures contrarily to its expected divergence at a quantum critical point. Above $T_{\mathbf{Q}}$, a $\mathbf{Q}$-dependent scaling behavior of the form $T\chi''(\mathbf{Q},E,T) = C_{\mathbf{Q}}f[E/(a_{\mathbf{Q}}T^{\beta_{\mathbf{Q}}})]$ with $\beta_{\mathbf{Q}}<1$ is obtained. This scaling does not enter the general framework of quantum phase transition theories, since it is obtained in a high temperature range, where Kondo spin fluctuations depend strongly on temperature.