Disorder-enhanced effective masses and deviations from Matthiessen's rule in PdCoO${}_2$ thin films

Abstract

The observation of hydrodynamic transport in the metallic delafossite PdCoO${}_2$ has increased interest in this family of highly conductive oxides, but experimental studies so far have mostly been confined to bulk crystals. In this work, the development of high-quality thin films of PdCoO${}_2$ has enabled a thorough study of the conductivity as a function of film thickness using both dc transport and time-domain THz spectroscopy. With increasing film thickness from 12 nm to 102 nm, the residual resistivity decreases and we observe a large deviation from Matthiessen's rule (DMR) in the temperature dependence of the resistivity. We find that the complex THz conductivity is well fit by a single Drude term. We fit the data to extract the spectral weight and scattering rate simultaneously. The temperature dependence of the Drude scattering rate is found to be nearly independent of the residual resistivity and cannot be the primary mechanism for the observed DMR. Rather, we observe large changes in the spectral weight as a function of disorder, changing by a factor of 1.5 from the most disordered to least disordered films. We believe this corresponds to a mass enhancement of $\ge 2$ times the value of the bulk effective mass which increases with residual disorder. This suggests that the mechanism behind the DMR observed in dc resistivity is primarily driven by changes in the electron mass. We discuss the possible origins of this behavior including the possibility of disorder-enhanced electron-phonon scattering, which can be systematically tuned by film thickness.

arXiv comment10 pages, 8 figures

References in corpus (19)

• Evidence for hydrodynamic electron flow in PdCoO${}_2$
• Hydrodynamic Electron Flow and Hall Viscosity
• The properties of ultrapure delafossite metals
• Quantum oscillations and high carrier mobility in the delafossite PdCoO${}_2$
• Disorder in quantum many-body systems
• Transport properties of strongly coupled electron-phonon liquids
• Electromagnetic properties of viscous charged fluids
• Highly conductive PdCoO2 ultrathin films for transparent electrodes
• Electron-phonon hydrodynamics
• Universal linear and nonlinear electrodynamics of the Dirac fluid
• Electron hydrodynamics with a polygonal Fermi surface
• Growth of metallic delafossite PdCoO2 by molecular beam epitaxy
• Quantum Order-by-Disorder in Strongly Correlated Metals
• Super-geometric electron focusing on the hexagonal Fermi surface of PdCoO${}_2$
• $h/e$ Oscillations in Interlayer Transport of Delafossites
• Large anisotropic thermal conductivity of intrinsically two-dimensional metallic oxide PdCoO${}_2$
• Quasiparticle interference and quantum confinement in a correlated Rashba spin-split 2D electron liquid
• Perfect separation of intraband and interband excitations in PdCoO${}_2$
• Drag viscosity of metals and its connection to Coulomb drag