Temperature-dependent optical properties of self-doped superconducting Fe-pnictide, Sr2VO3FeAs

We performed an 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 [SrVO3] (-1) and [SrFeAs](+1). Since the typical size of single crystalline Sr2VO3FeAs samples is 200 x 200 x 10 mu m(3) an optical study on this material is challenging. We observed an additional interband transition around 1000 cm(-1), which is absent in other doped Ba-122 Fe-pnictides. The origin of this additional transition is not clearly known yet. We also observed a hidden Fermi liquid behavior. Interestingly, we observed a Fano line-shaped phonon which appears near 555 cm(-1) below 200 K and shows a strong blue-shift when the temperature is lowered. The amplitude, width, and asymmetric Fano parameter of this phonon show anomalies at 150 K, which are probably related to an electronic phase observed below 155 K recently by an NMR study (Ok el al 2017 Nat. Commun. 8 2167). Our finding may help to understand the electronic phase observed previously in the same material. © 2019 IOP Publishing Ltd Printed in the UK11sciescopu