# Pressure dependent intermediate valence behavior in YbNiGa$_{4}$ and YbNiIn$_{4}$

## TL;DR

This study investigates how pressure influences the valence state of Yb in YbNiGa4 and YbNiIn4, revealing continuous valence changes, a possible electronic transition, and the importance of lattice and chemical effects.

## Contribution

It provides the first detailed pressure-dependent valence analysis of YbNiGa4 and YbNiIn4, highlighting the limitations of DFT in capturing valence drops and emphasizing the roles of lattice and chemical environment.

## Key findings

- YbNiGa4 shows steady Yb-valence increase with pressure, saturating around 25 GPa.
- YbNiIn4 exhibits a pressure-induced electronic topological transition near 10-14 GPa.
- Yb-valence drops sharply at certain Yb-Yb spacings, not predicted by DFT.

## Abstract

We report a comprehensive structural and valence study of the intermediate valent materials YbNiGa$_{4}$ and YbNiIn$_{4}$ under pressures up to 60 GPa. YbNiGa$_{4}$ undergoes a smooth volume contraction and shows steady increase in Yb-valence with pressure, though the Yb-valence reaches saturation around 25 GPa. In YbNiIn$_{4}$, a change in pressure dependence of the volume and a peak in Yb-valence suggest a pressure induced electronic topological transition occurs around 10-14 GPa. In the pressure region where YbNiIn$_{4}$ and YbNiGa$_{4}$ possess similar Yb-Yb spacings the Yb-valence reveals a precipitous drop. This drop is not captured by density-functional-theory calculations and implies that both the lattice degrees of freedom and the chemical environment play an important role in establishing the valence of Yb.