Magnetic and structural quantum phase transitions in CeCu6-xAux are independent

TL;DR

This study investigates CeCu6-xAux, revealing that magnetic and structural quantum phase transitions occur independently, with magnetic quantum criticality driven solely by magnetic fluctuations, unaffected by structural distortions.

Contribution

It provides evidence that magnetic and structural quantum phase transitions in CeCu6-xAux are decoupled, clarifying their independent roles in quantum critical behavior.

Findings

Magnetic and structural transitions are separated by pressure.

Magnetic quantum criticality is unaffected by structural distortion.

Magnetic fluctuations solely drive the quantum criticality.

Abstract

The heavy-fermion compound CeCu$_{6-x}$Au$_x$ has become a model system for unconventional magnetic quantum criticality. For small Au concentrations $0 \leq x < 0.16$, the compound undergoes a structural transition from orthorhombic to monoclinic crystal symmetry at a temperature $T_{s}$ with $T_{s} \rightarrow 0$ for $x \approx 0.15$. Antiferromagnetic order sets in close to $x \approx 0.1$. To shed light on the interplay between quantum critical magnetic and structural fluctuations we performed neutron-scattering and thermodynamic measurements on samples with $0 \leq x\leq 0.3$. The resulting phase diagram shows that the antiferromagnetic and monoclinic phase coexist in a tiny Au concentration range between $x\approx 0.1$ and $0.15$. The application of hydrostatic and chemical pressure allows to clearly separate the transitions from each other and to explore a possible effect of the structural transition on the magnetic quantum critical behavior. Our measurements demonstrate that at low temperatures the unconventional quantum criticality exclusively arises from magnetic fluctuations and is not affected by the monoclinic distortion.