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تسجيل مستخدم جديدOptical properties and electronic structure of the nonmetallic metal FeCrAs
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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 $Trightarrow T_N$ 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 Hunds 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.
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