Electronic structure of Gd-based intermetallics GdCu$_2$Ge$_2$ and GdCuAl$_3$

TL;DR

This study investigates the electronic structure of GdCu$_2$Ge$_2$ and GdCuAl$_3$ using temperature-dependent optical reflectivity, revealing distinct charge carrier behaviors and the impact of elemental substitution on their electronic properties.

Contribution

The paper provides a combined experimental and theoretical analysis of the electronic structure and charge dynamics in Gd-based intermetallics, highlighting the effects of doping and symmetry changes.

Findings

Two distinct charge carrier scattering rates observed.

Charge carriers in GdCuAl$_3$ are significantly suppressed, correlating with higher resistivity.

Elemental substitution acts as a Fermi level shift, with minor effects from symmetry changes.

Abstract

We present a temperature-dependent reflectivity study of single crystals of the ternary intermetallic compounds GdCu$_2$Ge$_2$ and GdCuAl$_3$ over a broad spectral range (100-18000 cm$^{-1}$, equivalent to 12 meV-2.23 eV) down to 13 K. Below 2000 cm$^{-1}$, the optical spectra are dominated by the response of itinerant charge carriers exhibiting two distinct scattering rates. While the response of the slow charge carriers shows negligible temperature dependence, the more mobile carriers follow the dc resistivity and are significantly suppressed in GdCuAl$_3$, consistent with the higher resistivity of this compound. We attribute this behavior to enhanced electronic correlations arising from the proximity of the Fermi level to van Hove singularities. Supported by density-functional-theory calculations, we further show that elemental substitution can be described as a rigid shift of the Fermi level, i.e., doping, whereas changes in the crystalline symmetry have only minor effects on the electronic structure.