Optical Spectroscopy Study Of The Collapsed Tetragonal Phase Of Cafe2(As0.935p0.065)(2) Single Crystals

We present an optical spectroscopy study on P-doped CaFe2As2 which experiences a structural phase transition from tetragonal to collapsed tetragonal (cT) phase near 75 K. The measurement reveals a sudden reduction of low-frequency spectral weight and the emergence of a feature near 3200 cm(-1) (0.4 eV) in optical conductivity across the transition, indicating an abrupt reconstruction of band structure. The appearance of the feature is related to the interband transition arising from the sinking of hole bands near the Gamma point below Fermi level in the cT phase, as expected from the density function theory calculations in combination with the dynamical mean field theory. However, the reduction of Drude spectral weight is at variance with those calculations. The measurement also indicates an absence of the abnormal spectral weight transfer at high energy (near 0.5-0.7 eV) in the cT phase, suggesting a suppression of the electron correlation effect.