Quantum oscillations and quasiparticle properties of thin film Sr2RuO4

Abstract

We measure the Shubnikov--de Haas effect in thin-film ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ grown on an $({\mathrm{LaAlO}}_{3}{)}_{0.29}\text{\ensuremath{-}}({\mathrm{SrAl}}_{1/2}{\mathrm{Ta}}_{1/2}{\mathrm{O}}_{3}{)}_{0.71}$ substrate. We detect all three known Fermi surfaces and extract the Fermi surface volumes, cyclotron effective masses, and quantum lifetimes. We show that the electronic structure is nearly identical to that of single-crystal ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, and that the quasiparticle lifetime is consistent with the ${T}_{\mathrm{c}}$ of comparably clean, single-crystal ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$. Unlike single-crystal ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, where the quantum and transport lifetimes are roughly equal, we find that the transport lifetime is $1.3\ifmmode\pm\else\textpm\fi{}0.1$ times longer than the quantum lifetime. This may suggest that extended (rather than point) defects could be the dominant source of quasiparticle scattering in these films. To test this hypothesis, we perform cross-sectional scanning transmission electron microscopy and find that out-of-phase boundaries extending the entire thickness of the film occur with a density that is consistent with the quantum mean free path. The long quasiparticle lifetimes make these films ideal for studying the unconventional superconducting state in ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ through the fabrication of devices---such as planar tunnel junctions and superconducting quantum interference devices.