Directional Anomalous Skin Effect in ReO₃

Rhenium oxide (ReO₃) is the most highly conducting oxide material due to its extraordinarily low residual resistivity[1]. Due to this property it has a remarkably long low-temperature electronic mean free path, similar to that seen in the ultrapure delafossites. Recent observations from broadband microwave spectroscopy have revealed a new directional anomalous skin effect (ASE) in the quasi-2D delafossite material palladium cobaltate (PdCoO₂)[2]. This effect has also been found in ReO₃. The anisotropic ASE response in these materials is influenced by the alignment of surface currents, the electromagnetic wavevector, and the facets on their Fermi surfaces. For PdCoO₂, recent nonlocal Boltzmann transport models for anisotropic metals accurately describe its behaviour, which falls between the ballistic and hydrodynamic electronic transport regimes[3,4].<br/><br/>However, the directional ASE in ReO₃ has more complexity due to its three-dimensional electronic structure and multiple Fermi surface sheets. In this study, we provide microwave spectroscopy results for high-purity single-crystal samples of ReO₃ at low temperatures. These results demonstrate the unique anisotropy that arises for surface currents flowing in different directions with respect to the Fermi surface facets. Our findings confirm the directional ASE in ReO₃, and we interpret these results using nonlocal skin effect transport models.<br/> <br/>[1] J. Falke et al., Phys. Rev. B <b>103</b>, 115125 (2021).<br/>[2] G. Baker, T. W. Branch et al., arXiv:<b>2204</b>.14239 (2023).<br/>[3] D. Valentinis et al. Phys. Rev. Research <b>5</b>(1), 013212 (2023).<br/>[4] G. Baker, University of British Columbia, Dissertation (2022).