Optical properties of the spin-ladder compound Sr14Cu24O41

Laboratorium voor Vaste-Stoffysica en Magnetisme, K. U. Leuven, B-3001, Leuven, Belgium; Max-Planck-Institut für Festkörperforschung, D-70569, Stuttgart, Germany; Institute of Physics, P.O. Box 68, 11080, Belgrade, Yugoslavia; Physics Department, Moscow State University, 119899, Moscow, Russia
Physical Review B (Impact Factor: 3.66). 01/2000; 62(8):4963-4972. DOI: 10.1103/PhysRevB.62.4963
Source: arXiv

ABSTRACT We report the measurements of the pseudodielectric function, far-infrared reflectivity, 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 measurements yield the gap values of 1.4, 1.86, 2.34 eV (2.5 eV) for the ladders (chains) along the c axis and 2.4 eV along the a axis. The electronic structure 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=t0=0.26 eV, along and perpendicular to legs, txy=0.026 eV (interladder hopping) and U=2.1 eV, as a Coulomb repulsion. The optical parameters of the infrared-active phonons and plasmons are obtained by an oscillator fitting procedure of the reflectivity spectra. Raman scattering spectra are measured at different temperatures using different laser line energies. The two-magnon peak is observed at about 2880 cm-1. At temperatures below 150 K the new infrared and Raman modes appear due to the charge ordering.


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