Spin-density-wave-induced anomalies in the optical conductivity of AFe sub(2)As sub(2) (A = Ca, Sr, Ba) single-crystalline iron pnictides

We report the complex dielectric function of high-quality AFe[sub 2]As[sub 2], single crystals with T[subN] = 150 K, 200 K, and 138 K, respectively, determined by broadband spectroscopic ellipsometry at temperatures 10[< or =]T[< or =] K and wave numbers from 100 cm[sup -1] to 52000 cm[sup -1]. In CaFe[sub 2]As[sub 2] we identify the optical spin-density-wave gap 2 Delta [subSDW] = 1250 cm[sup -1]. Our results single out CaFe[sub 2]As[sub 2] in the class of type ThCr[sub 2]Si[sub 2]-type iron-based materials by demonstrating the existence of two weakly coupled and extremely metallic electronic subsystems.