EVIDENCE FOR STRONG ELECTRON-PHONON COUPLING AND POLARONS IN THE OPTICAL-RESPONSE OF LA2-XSRXCUO4

The normal state optical response of La2-xSrxCuO4 is found to be consi stent with a multi-component model, based on free carriers with strong electron-phonon interaction, localized polaronic states near 0.15 eV, and a mid-infrared band at 0.5 eV, Based on experimental results in u nderdoped samples, the normal state reflectance and absorbance of La1. 83Sr0.17CuO4 are investigated and both AC and DC response are recovere d, The quasi-linear behavior of the optical scattering rate up to 3000 -4000 cm(-1) is found to be consistent with strong electron-phonon int eraction, which also accounts for the value of T-c. Investigations of superconducting state data indicate a weak temperature dependence of t he 0.5 eV MIR band, supporting a bipolaronic origin of this band, and suggest that the gap symmetry in LSCO is more complicated than simple s-wave. (C) 1997 Elsevier Science B.V.