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

M. Pinterić, M. Dressel, M. Wenzel, P. Puphal

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.

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

Abstract

We present a temperature-dependent reflectivity study of single crystals of the ternary intermetallic compounds GdCuGe and GdCuAl over a broad spectral range (100-18000 cm, equivalent to 12 meV-2.23 eV) down to 13 K. Below 2000 cm, 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, 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.
Paper Structure (7 sections, 2 equations, 4 figures, 2 tables)

This paper contains 7 sections, 2 equations, 4 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Methods
  3. Synthesis and characterization
  4. Optical measurements
  5. Computational
  6. Results and Discussion
  7. Conclusions

Figures (4)

  • Figure 1: (a, b) Crystal structures of GdCu$_2$Ge$_2$ and GdCuAl$_3$, respectively, visualized with VESTAMomma2008. (c, d) Photographs of the single crystals used in the optical experiments prior to polishing. Backscattered x-ray Laue images of the same crystals are given in panels (e-h), confirming the tetragonal symmetry.
  • Figure 2: Dc resistivity curves of GdCu$_2$Ge$_2$ (a) and GdCuAl$_3$ (b) measured in the $ab$-plane and normalized to the resistivity values obtained from our optical measurements via Hagen-Rubens fits. The kinks at low temperatures, highlighted in the insets, correspond to the antiferromagnetic transitions at $T_{\mathrm{N}} = 10$ K and 12 K of GdCu$_2$Ge$_2$ and GdCuAl$_3$, respectively. Panels (c) and (d) show the in-plane reflectivity of GdCu$_2$Ge$_2$ and GdCuAl$_3$ at selected temperatures, while panels (e) and (f) present the corresponding calculated real part of the optical conductivity.
  • Figure 3: Optical conductivity of GdCu$_2$Ge$_2$ (a) and GdCuAl$_3$ (b) at 13 K, modeled using two Drude contributions (blue and pink) and several Lorentzians above 2000 cm$^{-1}$, describing the interband transitions (orange).
  • Figure 4: (a, b) Experimental interband optical transitions of GdCu$_2$Ge$_2$ and GdCuAl$_3$ at 13 K, respectively, obtained by subtracting the Drude contributions form the spectra. (c, d) Calculated band-resolved optical conductivities with different colors marking interband transitions across different bands labeled in the band structures in panels (e) and (f).