# Strange metal behavior in a pure ferromagnetic Kondo lattice

## TL;DR

This paper provides evidence that a ferromagnetic heavy fermion compound exhibits strange metal behavior at a quantum critical point, challenging the common association of strange metals with antiferromagnetic quantum criticality and highlighting the role of magnetic anisotropy and entanglement.

## Contribution

It demonstrates that ferromagnetic quantum critical points can host strange metal phases, revealing a new setting for understanding quantum entanglement's role in strange metallic behavior.

## Key findings

- Strange metal phase observed at the pressure-induced QCP in CeRh6Ge4.
- Strong magnetic anisotropy injects entanglement into the ferromagnet.
- Transformation from triplet RVBs to Kondo singlets causes a Fermi surface jump.

## Abstract

The strange metal phases found to develop in a wide range of materials near a quantum critical point (QCP), have posed a long-standing mystery. The frequent association of strange metals with unconventional superconductivity and antiferromagnetic QCPs has led to a belief that they are highly entangled quantum states. Ferromagnets, by contrast are regarded as an unlikely setting for strange metals, for they are weakly entangled and their QCPs are often interrupted by competing phases or first order phase transitions. Here, we provide compelling evidence that the stoichiometric heavy fermion ferromagnet CeRh$_6$Ge$_4$ becomes a strange metal at a pressure-induced QCP: specific heat and resistivity measurements demonstrate that the FM transition is continuously suppressed to zero temperature revealing a strange metal phase. We argue that strong magnetic anisotropy plays a key role in this process,injecting entanglement, in the form of triplet resonating valence bonds (tRVBs) into the ordered ferromagnet. We show that the singular transformation from tRVBs into Kondo singlets that occurs at the QCP causes a jump in the Fermi surface volume: a key driver of strange metallic behavior. Our results open up a new direction for research into FM quantum criticality, while also establishing an important new setting for the strange metal problem. Most importantly, strange metallic behavior at a FM quantum critical point suggests that it is quantum entanglement rather than the destruction of antiferromagnetism that is the common driver of the many varied examples of strange metallic behavior.