Optical conductivity of single crystals of Na_(0.57)CoO_2

摘要

The optical conductivity of single crystals of Na_xCoO_2 (for x = 0.57) is reported between 295 and 30 K. In the far infrared, an "anomalous Drude" analysis leads to a carrier effective mass of 5 +- 1 electron masses. This high value is attributed to strong electron-phonon coupling, as suggested by the Fano distortion of a phonon at 570 cm~(-1). A peak at 8800 cm~(-1) scales with the charge transfer band of high-T_c cuprates by simply replacing the in-plane Cu-O bond length with that for Co-O.