Quantum Oscillations and the Quasiparticle Properties of Thin Film Sr$_2$RuO$_4$

TL;DR

This study measures quantum oscillations in thin-film Sr2RuO4, revealing electronic properties similar to single crystals and identifying defect-related scattering mechanisms, which makes these films promising for superconductivity research.

Contribution

First detailed quantum oscillation measurements in thin-film Sr2RuO4 showing comparable electronic structure to single crystals and insights into quasiparticle scattering sources.

Findings

Electronic structure nearly identical to single-crystal Sr2RuO4

Transport lifetime is longer than quantum lifetime, indicating extended defects

Presence of out-of-phase boundaries consistent with mean free path

Abstract

We measure the Shubnikov-de Haas effect in thin-film Sr$_2$RuO$_4$ grown on an (LaAlO$_3$)$_{0.29}$-(SrAl$_{1/2}$Ta$_{1/2}$O$_3$)$_{0.71}$ (LSAT) 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 Sr$_2$RuO$_4$, and that the quasiparticle lifetime is consistent with the Tc of comparably clean, single-crystal Sr$_2$RuO$_4$. Unlike single-crystal Sr$_2$RuO$_4$, where the quantum and transport lifetimes are roughly equal, we find that the transport lifetime is $1.3\pm0.1$ times longer than the quantum lifetime. This suggests that extended (rather than point) defects may be the dominant source of quasiparticle scattering in these films. To test this idea, we perform cross-sectional STEM 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 Sr$_2$RuO$_4$ through the fabrication of devices -- such as planar tunnel junctions and SQUIDs.