Tuning the electronic hybridization in the heavy fermion cage compound YbFe$_{2}$Zn$_{20}$ with Cd-doping

TL;DR

This study investigates how Cd doping in YbFe₂Zn₂₀ alters its heavy fermion behavior by weakening hybridization, causing a valence shift, and affecting magnetic and electrical properties, revealing insights into strongly correlated electron systems.

Contribution

It provides new understanding of how chemical pressure via Cd doping influences hybridization and valence states in YbFe₂Zn₂₀, a complex heavy fermion compound.

Findings

Cd doping expands the unit cell and weakens Yb 4f-conduction electron hybridization.

The Sommerfeld coefficient decreases with Cd doping, indicating reduced heavy fermion behavior.

DC resistivity decreases with Cd doping, suggesting a valence shift not related to charge doping.

Abstract

Tuning of the electronic properties of heavy fermion compounds by chemical substitutions provides excellent opportunities to further understand the physics of hybridized ions in crystal lattices. Here we present an investigation on the effects of Cd doping in flux-grown single crystals of the complex intermetallic cage compound YbFe$_{2}$Zn$_{20}$, that has been described as a heavy fermion with Sommerfeld coefficient of 535 mJ/mol.K$^{2}$. Substitution of Cd for Zn disturbs the system by expanding the unit cell and, in this case, the size of the Zn cages that surround Yb and Fe. With increasing amount of Cd, the hybridization between Yb $4f$ electrons and the conduction electrons is weakened, as evidenced by a decrease in the Sommerfeld coefficient, which should be accompanied by a valence shift of the Yb$^{3+}$ due to the negative chemical pressure effect. This scenario is also supported by the low temperature dc-magnetic susceptibility, that is gradually suppressed and evidences an increment of the Kondo temperature, based on a shift to higher temperatures of the characteristic broad susceptibility peak. Furthermore, the DC resistivity decreases with the isoelectronic Cd substitution for Zn, contrary to the expectation for an increasingly disordered system, and implying that the valence shift is not related to charge carrier doping. The combined results demonstrate excellent complementarity between positive physical pressure and negative chemical pressure, and point to a rich playground for exploring the physics and chemistry of strongly correlated electron systems in the general family of Zn$_{20}$ compounds, despite their structural complexity.