Abstract
The delafossite metals , , and are among the highest conductivity materials known, with low-temperature mean free paths of tens of microns in the best as-grown single crystals. A key question is whether these very low resistive scattering rates result from strongly suppressed backscattering due to special features of the electronic structure or are a consequence of highly unusual levels of crystalline perfection. We report the results of experiments in which high-energy electron irradiation was used to introduce point disorder to the Pd and Pt layers in which the conduction occurs. We obtain the cross section for formation of Frenkel pairs in absolute units, and cross-check our analysis with first-principles calculations of the relevant atomic displacement energies. We observe an increase of resistivity that is linear in defect density with a slope consistent with scattering in the unitary limit. Our results enable us to deduce that the as-grown crystals contain extremely low levels of in-plane defects of approximately 0.001%. This confirms that crystalline perfection is the most important factor in realizing the long mean free paths and highlights how unusual these delafossite metals are in comparison with the vast majority of other multicomponent oxides and alloys. We discuss the implications of our findings for future materials research.
- Received 12 December 2019
- Revised 11 March 2020
- Accepted 18 March 2020
DOI:https://doi.org/10.1103/PhysRevX.10.021018
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Why are some materials better electrical conductors than others? This seemingly fundamental question is surprisingly difficult to answer for many materials. One class of such enigmatic conductors is delafossite oxide metals—of all compound metals, this class has the highest conductivity known. Recent analyses have suggested that delafossite metals might get their high conductivity from a natural level of crystal purity that is never seen in fabricated crystals—a surprising claim that may open new avenues of research in quantum materials. To test that claim, we investigate how resistivity in several delafossite metals changes with crystalline disorder and find that these materials do exhibit extreme structural purity.
In our experiments, we grow three types of delafossite oxide metals. Using high-energy electrons, we control the density of displaced atoms (defects in the crystalline structure) in the samples. We find that the resistivity of the samples increases linearly with defect density, which allows us to deduce that untouched crystals have extremely low levels of defects, approximating just 0.001% of the material.
The unprecedented level of chemical perfection seems to be the key factor in the ultralow resistivity of delafossite oxide metals. Our work opens the way to similar investigations of other compounds, and we hope to use it to find other ultraperfect conductors.
