Hyperfine electro-nuclear coupling at the quantum criticality of YbCu4Zn

TL;DR

This study investigates hyperfine electro-nuclear coupling in YbCu4Zn near a quantum critical point, revealing weak coupling effects and deviations from standard nuclear specific heat behavior influenced by magnetic field application.

Contribution

It provides the first detailed analysis of hyperfine coupling effects in YbCu4Zn at quantum criticality, highlighting deviations from classical models due to weak electronic-nuclear interactions.

Findings

Logarithmic specific heat behavior indicating quantum criticality

Absence of RKKY interactions down to 0.03K

Deviation from 1/T^2 nuclear specific heat dependence

Abstract

An increasing number of Yb-based compounds fulfill the conditions for the investigation of hyperfine electro-nuclear coupling effects related to 171-Yb and 173-Yb isotopes. Among them, the lack of magnetic order down to the milikelvin range in compounds with robust localized electronic moments and their nuclear magnetism. Although reminiscences of short range magnetic interactions may be observed below 1K, such perturbation can be dodged investigating compounds located close to a quantum critical point (QCP), where quantum fluctuations prevent the development of magnetic correlations to develop. Within the family of cubic YbCu4M compounds (M = Ni, Au and Zn), we have investigated YbCu4Zn that shows a logarithmic temperature dependence: C_P /T ~ ln(T/TQ) in its electronic specific heat, as predicted for a QCP. Simultaneously, no signs of RKKY interactions are detected down to 0.03K. Due to the low Kondo temperature of its doublet ground state, the localized 4f electrons weakly couple with conduction electrons, allowing the coupling between nuclear and 4f electron moments to become relevant. However, the reminder Kondo interaction acts on the electronic hyperfine field producing a small deviation from the standard nuclear C_N ~ 1/T^2 dependence into a n < 2 power law. The expected n = 2 dependence is progressively recovered under applied magnetic field.