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The temperature dependence of the optical properties of EuCd₂P₂ have been determined over a wide frequency range for light polarized in the a-b planes.  At room temperature, the low-energy optical conductivity reveals two infrared-active lattice modes, one weak and one strong, superimposed on a weak electronic background, with σ₁(ω→0) ~30 Ω^-1cm^-1.  The conductivity can be reproduced reasonably well using a Drude-Lorentz model, yielding an estimate for the Drude plasma frequency ω_p,D ~1100 cm^-1 and scattering rate 1/τ_D ~800 cm^-1.  At about 18 K, well above the magnetic transition at T_N ~11 K, the free carriers become localized [1], likely due to the formation of ferromagnetic domains that result in spin-polarized clusters due to spin-carrier coupling [2]; however, below T_N metallic behavior is recovered.  We have attempted to map out these domains using an infrared microscope coupled to a synchrotron light source by studying the interaction of the high-frequency infrared mode with the electronic background.

 

[1] C. C. Homes, Z.-C. Wang, K. Fruhling, and F. Tafti, arXiv:2209.10606.

[2] V. Sunko et al., arXiv:2208.05499.