Tuning the electrical properties of superconducting Sr₂RuO₄ thin films by epitaxy

The superconducting phase of Sr₂RuO₄ is known to be unconventional and most likely odd-parity, but also the most sensitive to disorder of all known superconductors, requiring mean free paths of order ~ 100 nanometers. This has prompted work employing disorder-free knobs, such as externally applied strain both in single crystals and thin films, to manipulate and better understand the nature of the superconducting state that condenses from the low-temperature Fermi liquid in this multi-band system. Here we present a combination of x-ray diffraction and electrical transport measurements on strained thin films of Sr₂RuO₄ synthesized by molecular-beam epitaxy on various substrates and orientations to explore how the template set by the substrate can be used to control both the crystalline and defect structure of the films, as well as the material’s electronic response. Specifically, we probe how the substrate-induced lattice strain and planar defects modify the inelastic (electron-electron) and elastic (electron-disorder) scattering contributions to the electrical resistivity and anisotropy, and study their subsequent effects on superconductivity.