Optical properties of the spin-ladder compound Sr14Cu24O41

We report the measurements of the pseudodielectric function, far-infrared r eflectivity, and Raman scattering spectra in Sr14Cu24O41 single crystal. We study the lattice and the spin dynamics of the Cu2O3 spin ladders and CuO2 chains of this compound. The ellipsometric and the optical reflectivity me asurements yield the gap values of 1.4, 1.86, 2.34 eV (2.5 eV) for the ladd ers (chains) along the c axis and 2.4 eV along the a axis. The electronic s tructure of the Cu2O3 ladders is analyzed using the tight-binding approach for the correlated electron systems. The correlation gap value of 1.4 eV is calculated with the transfer energy (hopping) parameters t = t(0) = 0.26 e V, along and perpendicular to legs, t(xy) = 0.026 eV (interladder hopping) and U= 2.1 eV, as a Coulomb repulsion. The optical parameters of the infrar ed-active phonons and plasmons are obtained by an oscillator fitting proced ure of the reflectivity spectra. Raman scattering spectra are measured at d ifferent temperatures using different laser line energies. The two-magnon p eak is observed at about 2880 cm(-1). At temperatures below 150 K the new i nfrared and Raman modes appear due to the charge ordering.