Temperature-dependent optical properties of Sr₂VO₃FeAs

We performed infrared spectroscopic study on a single crystal of Sr₂VO₃FeAs grown by a self-flux method. This layered material system consists of two alternative layers of Sr₂VO₃ and FeAs. Since the typical size of single crystalline Sr₂VO₃FeAs samples is 200 x 200 x 10 μm³ optical study on this material is challenging. We could measure reflectance spectra of ab-plane at various temperatures from 8 K to 300 K using an in-situ gold evaporation technique in far- and mid-infrared regions. This material shows dc resistivity and magnetic susceptibility anomalies near 155 K. We observed that a Fano-shaped phonon appears below 200 K and shows a strong blue-shift with lowering the temperature. We also observed an additional interband transition around 1000 cm^-1, which is absent in other doped Ba-122 Fe-pnictides. We will discuss about further issues on this material.