Electronic Structure of Epitaxial Films of the Bilayer Strontium Ruthenate: Sr$_{3}$Ru$_2$O$_{7}$

Abstract

We report the first combined study of the low-energy electronic band structure of epitaxial Sr$_3$Ru$_2$O$_7$ films using angle-resolved photoemission spectroscopy and density functional theory. The complete Fermi-surface topography of the near-Fermi-level bands is determined from in-situ ARPES measurements. To investigate the effects of substrate-induced strain on the band structure, Sr$_3$Ru$_2$O$_7$ thin films are epitaxially grown on SrTiO$_3$ and (LaAlO$_{3}$)$_{0.3}$(Sr$_{2}$TaAlO$_{6}$)$_{0.7}$ substrates using molecular beam epitaxy. The combination of the measured Fermi-surfaces along with the theoretical interpretation, clearly show dramatic changes in the Fermi surface topologies that result from the underlying strain states of the films on the two substrates. We find that the Sr$_3$Ru$_2$O$_7$ films prepared on SrTiO$_3$ are tensile strained with tetragonal symmetry, whereas those grown on (LaAlO$_{3}$)$_{0.3}$(Sr$_{2}$TaAlO$_{6}$)$_{0.7}$ are compressively strained with orthorhombic symmetry. Within $\sim15~\text{meV}$ below the Fermi level, we observe two flat bands along $\Gamma$-$X$ in the orthorhombic phase and around $\Gamma$ in the tetragonal phase. These features could be favorable for van Hove singularities near the Fermi level, and highlight the emergence of magnetic instabilities in epitaxial Sr$_3$Ru$_2$O$_7$ films.