Temperature dependent Eu 3d-4f X-ray Absorption and Resonant Photoemission Study of the Valence Transition in $EuNi_2(Si_{0.2}Ge_{0.8})_2$

TL;DR

This study investigates the temperature-driven valence transition in EuNi2(Si0.2Ge0.8)2 using X-ray absorption and photoemission spectroscopy, revealing significant spectral changes and mixed valence behavior linked to hybridization and volume collapse.

Contribution

It provides detailed temperature-dependent spectroscopic analysis of the valence transition, highlighting the role of hybridization and Kondo-like effects in EuNi2(Si0.2Ge0.8)2.

Findings

Temperature-dependent spectral changes over 10 eV observed.

Mixed valence states identified at different temperatures.

Hybridization change linked to volume collapse inferred.

Abstract

We study the mixed valence transition ($T$$_{v}$ $\sim$80 K) in EuNi$_{2}$(Si$_{0.2}$Ge$_{0.8}$)$_{2}$ using Eu 3$d-4f$ X-ray absorption spectroscopy (XAS) and resonant photoemission spectroscopy (RESPES). The Eu$^{2+}$ and Eu$^{3+}$ main peaks show a giant resonance and the spectral features match very well with atomic multiplet calculations. The spectra show dramatic temperature ($T$)-dependent changes over large energies ($\sim$10 eV) in RESPES and XAS. The observed non-integral mean valencies of $\sim$2.35 $\pm$ 0.03 ($T$ = 120 K) and $\sim$2.70 $\pm$ 0.03 ($T$ = 40 K) indicate homogeneous mixed valence above and below $T$$_{v}$. The redistribution between Eu$^{2+}$$4f^7$+$[spd]^0$ and Eu$^{3+}$$4f^6$+$[spd]^1$ states is attributed to a hybridization change coupled to a Kondo-like volume collapse.