Raman scattering studies on the collapsed phase of CaCo<inf>2</inf>As<inf>2</inf>

Abstract

� 2016 Chinese Physical Society and IOP Publishing Ltd. In this work, Raman scattering measurements have been performed on the collapsed phase CaCo 2 As 2 crystals. At least 8 Raman modes were observed at room temperature though CaCo 2 As 2 is structurally similar to other 122 compounds like BaFe 2 As 2 . Two Raman modes are assigned to the intrinsic A 1g and B 1g of this material system respectively. The other ones are considered to originate from the local vibrations relevant to cobalt vacancies. Careful polarized measurements allow us to clearly resolve the four-fold symmetry of the B 1g mode, which put strong constraints on possible point group symmetries of the system with Co vacancies. The temperature-dependent measurements demonstrate that the anomalies in both frequency and width of the B 1g mode occur around Neel temperature T N . The anomalies are considered to be related to the gap opening near the magnetic transition. The study may shed light on the structural and magnetic changes and their correlations with superconductivity in 122 systems.