Scattering processes and magnon thermal conductivity in La5Ca9Cu24O41

We analyse the temperature dependence of the 1D magnon heat transport in La5Ca9Cu24O41 which contains undoped two-leg spinladders. In particular, we discuss possible scattering mechanisms which become relevant at elevated temperatures and thereby reduce the magnon thermal conductivity. Within the framework of a kinetic model, we find that the temperature dependence of the magnon mean free path lmag is well described if scattering of magnons by non-dispersive optical phonons is assumed. The phonon gap Δ≈800K extracted from the analysis is in good quantitative agreement with the energy of the Cu-O bond stretching modes in the ladder planes.