| Originally found as a peculiar byproduct of the extensive high-Tc superconductor research efforts, the spin ladder cuprate materials such as Ca9La5Cu24O41 constitute now an exciting field of research with its own intrinsic value. Their quantum disordered ground state properties and their intriguing magnetic excitation spectrum have been studied extensively. Also from an applicative point of view, these systems offer quite unusual properties. In particular, due to the high energy of the magnon excitations and their long mean free paths, these materials show an unusually high magnon-dominated thermal conductivity over a wide temperature range. Here we report unexpected large discrepancies between the static and dynamic thermal conductivity of Ca9La5Cu24O41. We propose that these discrepancies can be explained by considering an unusually long magnon-phonon coupling time originating from conservation of energy, momentum and spin in scattering processes. The results also show that measuring the dynamic thermal conductivity yields a useful probe for phonon-magnon interactions. |
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