Optical properties and electronic structure of the nonmetallic metal FeCrAs

Abstract

The complex optical properties of a single crystal of hexagonal FeCrAs ($T_N\simeq 125$ K) have been determined above and below $T_N$ over a wide frequency range in the planes (along the $b$ axis), and along the perpendicular ($c$ axis) direction. At room temperature, the optical conductivity ${\sigma }_1(\omega )$ has an anisotropic metallic character. The electronic band structure reveals two bands crossing the Fermi level, allowing the optical properties to be described by two free-carrier (Drude) contributions consisting of a strong, broad component and a weak, narrow term that describes the increase in ${\sigma }_1(\omega )$ below $\simeq 15$ meV. The dc-resistivity of FeCrAs is ``non-metallic'', meaning that it rises in power-law fashion with decreasing temperature, without any signature of a transport gap. In the analysis of the optical conductivity, the scattering rates for both Drude contributions track the dc-resistivity quite well, leading us to conclude that the non-metallic resistivity of FeCrAs is primarily due to a scattering rate that increases with decreasing temperature, rather than the loss of free carriers. The power law ${\sigma }_1(\omega )\propto {\omega }^{-0.6}$ is observed in the near-infrared region and as $T\to T_N$ spectral weight is transferred from low to high energy ($\gtrsim 0.6$ eV); these effects may be explained by either the two-Drude model or Hund's coupling. We also find that a low-frequency in-plane phonon mode decreases in frequency for $T<T_N$, suggesting the possibility of spin-phonon coupling.

9 pages, 8 figures and 3 tables; added DFT calculations, analyzed data using two-Drude model

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Cited by in corpus (8)

• On infrared pseudogap in cuprate and pnictide high-temperature superconductors
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• Local magnetism, magnetic order and spin freezing in the 'nonmetallic metal' FeCrAs
• From mean-field localized magnetism to itinerant spin fluctuations in the "Non-metallic metal" - FeCrAs
• Spin reorientation in FeCrAs revealed by single-crystal neutron diffraction
• Persistent antiferromagnetic order in heavily overdoped Ca${}_{1-x}$La${}_x$FeAs${}_2$
• Honeycomb lattice iridate on the verge of Mott-collapse
• Enhanced Neel temperature and unusual thermal expansion in flux-grown FeCrAs crystals