Single-crystal growth and optical conductivity of SrPt2As2superconductors

Abstract

SrPt${}_{2}$As${}_{2}$ single crystals with CaBe${}_{2}$Ge${}_{2}$-type structure were synthesized by self-melting technique. X-ray diffraction, transmission electron microscopy, electrical resistivity, magnetic susceptibility, specific heat, and optical spectroscopy measurements were conducted to elucidate the properties of SrPt${}_{2}$As${}_{2}$. SrPt${}_{2}$As${}_{2}$ single crystals undergo a structural phase transition well above room temperature (about 450 K) and become superconducting at 5.18 K. The superconducting and structural phase transition temperatures are reduced by 6$%$ iridium doping. Both the pure SrPt${}_{2}$As${}_{2}$ and the Ir-doped single crystals are demonstrated to be highly metallic with rather high plasma frequencies. In particular, the optical spectroscopy measurement revealed two gaplike suppression structures: a stronger one at high energy near 12 000 cm${}^{\ensuremath{-}1}$ ($\ensuremath{\sim}$1.5 eV), and a less prominent one at lower energy near 3200 cm${}^{\ensuremath{-}1}$ ($\ensuremath{\sim}$0.4 eV) for the pure compound. We elaborate that the former is related to the correlation effect, while the latter could be attributed to the partial energy gap formation associated with structural phase transition.