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Rhenium oxide (ReO₃) is the most conductive oxide material due to its exceptionally low residual resistivity[1]. This property endows it with an incredibly long low-temperature electronic mean free path, similar to the ultrapure delafossites. Recent observations from broadband microwave spectroscopy have shown a novel directional anomalous skin effect (ASE) in the quasi-2D delafossite material palladium cobaltate (PdCoO₂)[2]. This effect has also been detected in ReO₃. The anisotropic ASE response in these materials is influenced by the relative alignment of surface currents and the facets on their Fermi surfaces. For PdCoO₂, recent nonlocal Boltzmann transport models aptly describe its behaviour, indicating that it falls between the ballistic and hydrodynamic electronic transport regimes[3,4].

However, the directional ASE in ReO₃ exhibits more intricacy due to its 3D electronic structure and multiple Fermi surface sheets. In this study, we provide microwave spectroscopy results for high-purity samples of ReO₃ at low temperatures. These results reveal the rich anisotropy that arises for surface currents flowing in different crystallographic directions. Our findings confirm the directional ASE in ReO₃, and we interpret these results using transport models.

[1] J. Falke et al., Phys. Rev. B 103, 115125 (2021)

[2] G. Baker, T. W. Branch et al., arXiv:2204.14239 (2023)

[3] D. Valentinis et al., Phys. Rev. Research 5(1), 013212 (2023)

[4] G. Baker, University of British Columbia, Dissertation (2022)