Anomalous transport in distorted-kagome-lattice TT'X intermetallics

There has been a lot of interest in the physics of kagome lattice intermetallics, whose band structure has topological features and flat bands, giving rise to density waves, anomalous Hall resistivity, and exotic superconductivity. I will discuss a family of (possibly) related, distorted-kagome-lattice compounds, that also display unusual transport properties. They have chemical formula TT'X, where T and T' are transition metals, and X is arsenic or phosphorus, and P62m symmetry. This family includes, for example CrNiAs, which was recently shown to have a large anomalous Hall effect [1,2] and strange metal behavior at a pressure-induced quantum critical point [2]. After a general overview, I will focus on the compounds CrFeAs and CrPdAs, which show 'non-metallic' in-plane resistivity, by which we mean resistivity with a negative temperature coefficient over the entire measured temperature range, which extends up to 800 K in the case of CrFeAs [3]. These two materials have contrasting levels of disorder, but otherwise rather similar properties. Both systems show magnetic order, in one case antiferromagnetism and in the other spin-glass freezing, that seems to be ignored by the in-plane resistivity. Moreover, below about 130 K the in-plane resistivity of CrPdAs rises linearly with decreasing temperature, which is a rare phenomenon. Finally, while CrFeAs does not have an anomalous Hall effect, CrPdAs has a large AHE, despite not ordering ferromagnetically.

[1] Pressure-induced strange metal phase in a metallic kagome ferromagnet, B. Shen, F. Du, F. Breitner, V.A. Ginga, E. Uykur, A.A. Tsirlin and P. Gegenwart, arXiv:2503.09524.
[2] Anomalous electronic transport in hexagonal ternary arsenides FeCrAs, CrNiAs and CrPdAs, B. Lau (2024) (Ph D Thesis, University of Toronto)
[3] A novel non-Fermi-liquid state in the iron pnictide FeCrAs, W. Wu, A. McCollam, I. Swainson, P.M.C. Rourke, D.G. Rancourt and S.R. Julian, Eur. Phys. J. 85 (2009) 17009.
[4] Quasi-linear ‘non-metallic’ resistivity in the distorted-kagome metal CrPdAs, B. Lau, W. Wu, B. Yuan, J. Nickel, and S.R. Julian, arXiv:2604:11630