Unconventional magneto-transport in ultrapure PdCoO2 and PtCoO2

Abstract

The single-band, quasi-two dimensional metals PdCoO₂ and PtCoO₂ have recently come to prominence because of their extremely long mean free paths, which establish them as some of the most electronically pure materials known, and as potential hosts of previously unobservable regimes of electronic transport. To fully establish their magnetotransport properties, we have studied the magnetoresistance and Hall effect in bulk single crystals to which electrical contacts have been made with high precision using focused ion beam machining. We observe a strong temperature dependence of the Hall resistivity in small applied fields, linked to a large violation of Kohler’s rule in the magnetoresistance. We discuss the extent to which these observations can be accounted for by standard transport theory.

Quantum transport: benchmarks

A magneto-transport experiment on ultra-pure PdCoO₂ and PtCoO₂ establishes a baseline for comparison to more exotic materials. An international team lead by Nabhanila Nandy and Andrew Mackenzie from the Max Planck Institute for Chemical Physics of Solids have carefully analysed the magneto-resistance of these materials and compared to standard theoretical descriptions. They find a strong temperature dependence, which reveals that more than one microscopic length scale is controlling the electron scattering. The Drude transport theory cannot account for this, and explaining it within Boltzmann theory requires some assumptions that need further theoretical support. Given the recent interest in exotic quantum transport–such as hydrodynamic electron flow or the very low resistivity measured in Dirac and Weyl semimetals–these results provide a reference for future work.