Ferromagnetic Quantum Criticality in the Quasi-One-Dimensional Heavy Fermion Metal YbNi4P2

TL;DR

YbNi4P2 is a quasi-one-dimensional heavy-fermion metal exhibiting ferromagnetic quantum criticality at an extremely low temperature, with unconventional divergence in thermodynamic and transport properties, making it a unique system for studying quantum critical phenomena.

Contribution

This study introduces YbNi4P2 as a new clean ferromagnetic heavy-fermion system with unique quantum critical behavior and strong electronic correlations.

Findings

Ferromagnetic transition at T_C=0.17K with small ordered moment

Diverging susceptibility and enhanced Sommerfeld coefficient

Linear-in-T resistivity above T_C

Abstract

We present a new Kondo-lattice system, YbNi4P2, which is a clean heavy-fermion metal with a severely reduced ferromagnetic ordering temperature at T_C=0.17K, evidenced by distinct anomalies in susceptibility, specific-heat, and resistivity measurements. The ferromagnetic nature of the transition, with only a small ordered moment of ~0.05mu_B, is established by a diverging susceptibility at T_C with huge absolute values in the ferromagnetically ordered state, severely reduced by small magnetic fields. Furthermore, YbNi4P2 is a stoichiometric system with a quasi-one-dimensional crystal and electronic structure and strong correlation effects which dominate the low temperature properties. This is reflected by a stronger-than-logarithmically diverging Sommerfeld coefficient and a linear-in-T resistivity above T_C which cannot be explained by any current theoretical predictions. These exciting characteristics are unique among all correlated electron systems and make this an interesting material for further in-depth investigations.