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

Sethulakshmi Sajeev, Arnaud P. Nono Tchiomo+11 more|arXiv (Cornell University)|Feb 8, 2026

Electronic and Structural Properties of Oxides0 citations

TL;DR

The paper combines in-situ ARPES and DFT to map the low-energy electronic structure and Fermi-surface topology of epitaxial Sr3Ru2O7 thin films under strain from two substrates, revealing strain-driven symmetry changes and near-EF flat bands that suggest potential magnetic instabilities.

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 $\sim15~ ext{meV}$ below the Fermi level, we observe two flat bands along $Γ$-$X$ in the orthorhombic phase and around $Γ$ 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.

Motivation & Objective

• Investigate how substrate-induced strain modifies the electronic band structure of Sr3Ru2O7 bilayer films.
• Determine the complete Fermi-surface topology of near-EF bands in epitaxial Sr3Ru2O7.
• Assess the influence of epitaxial strain on crystal symmetry and octahedral rotations in thin films.
• Compare ARPES-derived Fermi surfaces with DFT calculations incorporating measured lattice parameters.
• Explore potential van Hove singularities and their relation to magnetic instabilities in strained films.

Proposed method

• Grow Sr3Ru2O7 thin films by molecular beam epitaxy on STO (tensile, tetragonal) and LSAT (compressive, orthorhombic) substrates.
• Characterize strain and symmetry via reciprocal space maps and XRD (Kiessig fringes indicate high-quality interfaces).
• Perform in-situ ARPES at 7 K with 5 meV energy resolution to map the Fermi surface and band dispersions.
• Compute DFT band structures using pseudopotential plane-wave methods with lattice parameters from RSM to reflect strain states.
• Include spin–orbit coupling and consider octahedral rotation patterns to reproduce folded Brillouin zones and FS features.
• Correlate experimental ARPES data with DFT bands to interpret orbital character and bilayer splitting.

Figure 1: (a) Crystal structure of bilayered ruthenate Sr 3 Ru 2 O 7 in the tetragonal I4/mmm phase. The blue contour encompasses the unit cell. (b) Schematic of the photoexcitation process in ARPES experiments viewed from the sample surface. The emission angle, $\theta$ , the sample rotation angle,

Experimental results

Research questions

• RQ1 How does tensile vs compressive epitaxial strain alter the Fermi-surface topology of Sr3Ru2O7 thin films?
• RQ2 Do strained Sr3Ru2O7 films exhibit orthorhombic or tetragonal symmetry, and how does this reflect in octahedral rotations and Brillouin-zone folding?
• RQ3 Are there near-EF flat bands or van Hove-like features that could promote magnetic instabilities under strain?
• RQ4 To what extent do DFT calculations replicate the ARPES-measured electronic structure when lattice parameters are taken from strain-informed RSM data?
• RQ5 What are the orbital characters and bilayer-splitting features observable in thin-film Sr3Ru2O7 under different strain states?

Key findings

• Compressively strained (LSAT) films show orthorhombic symmetry with reconstructed Brillouin zone and backfolded bands.
• Tensile-strained (STO) films retain tetragonal-like symmetry with reduced octahedral rotation and less Brillouin-zone folding.
• DFT bands calculated using RSM-derived lattice parameters reproduce the main ARPES features, including observed Fermi-surface pockets and bilayer effects.
• Near EF (within ~15 meV) there are two flat bands along Γ–X in the orthorhombic phase and near Γ in the tetragonal phase, suggesting proximity to van Hove singularities.
• Some predicted pockets (e.g., δ pocket in orthorhombic phase) are not clearly resolved in ARPES, likely due to low spectral weight and film disorder, while a flat Γ-centered feature in the tetragonal phase appears unaccounted for by the calculated bands.
• The study indicates strong sensitivity of Sr3Ru2O7 electronic structure to epitaxial strain and supports the potential for strain-engineered magnetic instabilities.

Figure 2: (a) Symmetrized ARPES Fermi-surface map of Sr 3 Ru 2 O 7 grown on LSAT. The white square marks the reconstructed Brillouin zone arising from octahedral rotations. (b) Calculated Fermi surface of Sr 3 Ru 2 O 7 for LSAT-induced strain, which drives the system into an orthorhombic structure.