Crossover from a heavy fermion to intermediate valence state in noncentrosymmetric Yb2Ni12(P,As)7

TL;DR

This study investigates the electronic and structural evolution in Yb2Ni12(P,As)7 compounds, revealing a crossover from intermediate valence to heavy-fermion states and identifying a potential quantum critical point under pressure.

Contribution

It provides new insights into the valence crossover and quantum criticality in noncentrosymmetric Yb compounds through comprehensive measurements and analysis.

Findings

Yb2Ni12As7 exhibits intermediate valence, Yb2Ni12P7 shows heavy-fermion behavior.

Pressure suppresses Fermi liquid temperature in Yb2Ni12P7, indicating a quantum critical point.

Valence and lattice anomalies in Yb2Ni12As7 suggest structural-electronic correlations.

Abstract

We report measurements of the physical properties and electronic structure of the hexagonal compounds Yb2Ni12Pn7 (Pn = P, As) by measuring the electrical resistivity, magnetization, specific heat and partial fluorescence yield x-ray absorption spectroscopy (PFY-XAS). These demonstrate a crossover upon reducing the unit cell volume, from an intermediate valence state in Yb2Ni12As7 to a heavy-fermion paramagnetic state in Yb2Ni12P7, where the Yb is nearly trivalent. Application of pressure to Yb2Ni12P7 suppresses T_FL, the temperature below which Fermi liquid behavior is recovered, suggesting the presence of a quantum critical point (QCP) under pressure. However, while there is little change in the Yb valence of Yb2Ni12P7 up to 30 GPa, there is a strong increase for Yb2Ni12As7 under pressure, before a near constant value is reached. These results indicate that any magnetic QCP in this system is well separated from strong valence fluctuations. The pressure dependence of the valence and lattice parameters of Yb2Ni12As7 are compared and at 1 GPa, there is an anomaly in the unit cell volume as well as a change in the slope of the Yb valence, indicating a correlation between structural and electronic changes.