Refined Epitaxial Growth of YbRh₂Si₂ Thin Films

Abstract

Epitaxial thin films of the heavy fermion compound YbRh₂Si₂ have opened new possibilities in the investigation of the enigmatic strange metal state, including terahertz transmission spectroscopy and shot noise. For experiments at lower temperatures and energies, further advances in film quality are desirable. In this work, The focus is on the enhancement of crystallinity and surface smoothness of YbRh₂Si₂ thin films grown by molecular beam epitaxy using Knudsen cells and electron-beam evaporation sources. The morphology is influenced by the Yb flux and provides insight into the crystal quality of the thin films confirmed by in-plane and out-of-plane diffraction techniques. Changes in the surface morphology affect the physical characteristics of the film. A nucleation study is performed with the assistance of ab initio calculations of the binding energy of each element, i.e., Yb, Rh, and Si, with the substrate and permits to further reduce the surface roughness of the films and refinement of crystal quality, as evidenced by sharper peaks in X-ray diffraction scans. The residual resistance ratio depends linearly on the lattice mismatch. At low temperatures, the electrical resistivity of the best epitaxial thin films exhibits a linear-in-temperature dependence characteristic of strange metals.