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The temperature dependence of the optical properties of the layered material EuCd₂P₂ have been determined over a wide frequency range for light polarized in the planes.  At room temperature, the low-energy optical conductivity reveals two infrared-active E_u vibrational modes (one weak, the other very strong) superimposed on a weak electronic background, with σ₁(ω→0) ~30 Ω^-1cm^-1.  At high temperature the optical conductivity can be reproduced reasonably well using a Drude-Lorentz model for the dielectric function, yielding an estimate for the Drude plasma frequency ω_p,D ~1700 cm^-1 and scattering rate 1/τ_D ~1600 cm^-1.  In the far-infrared region the conductivity increases with decreasing temperature until just above the magnetic transition at T_N ~11 K, where it decreases dramatically, but recovers by 5 K, in good agreement with transport measurements [1].  It is proposed that the decrease in optical conductivity is due to carrier localization driven by strong antiferromagnetic fluctuations.

 

[1] Z.-C. Wang et al., Adv. Mater. 33, 2005755 (2021).