Intermediate dimensional character of charge transfer excitation modes in a two-leg cuprate ladder

Abstract

Collective charge modes in the cuprate ladder compound Sr 14 Cu 24 O 41 are studied over the one-dimensional Brillouin zone using resonant inelastic X-ray scattering. Low energy (2–4 eV) spectral weight across the Mott gap is dominated by a broad, dispersive feature containing two distinct peaks that may be interpreted as independent modes. Details of low energy dispersion, intensity distribution across the Brillouin zone and peak composition fall between the characteristic spectra of quasi-1D (e.g. SrCuO 2) and -2D cuprates (e.g. Nd 2CuO 4). We demonstrate that dispersion and splitting between the two observed modes can be understood in a variant of the strong coupling limit (Hubbard- U ⪢ t ) with a single band Hubbard model.