Effect of impurity scatterers on phonon, electron and magnon thermal transport in electron doped cuprate superconductors

A theoretical model is evolved to account for the anomalies reported for the thermal conductivity (?) of the electron doped cuprate superconductor Nd1.85Ce0.15CuO4. The lattice thermal conductivity by incorporating the scattering of phonons with defects, grain boundaries, electrons, and phonons in the model Hamiltonian is evaluated as a first step. Later on, the scattering of electrons with impurities for both s and d wave symmetry of the order parameter is also analysed. As a next step, the scattering of magnons with phonons, defects, grain boundaries and magnons is investigated in order to assess their role in thermal conduction. It is noticed that at very low temperatures (T<10?K), ? increases and shows almost T3/2 dependence on the temperature, which is attributed to spin-wave transport. However, the inclusion of phonon?impurity and the carrier?impurity scattering reduces the temperature dependence of ? and a power temperature dependence is revealed for T<10?K. Further, at Tc, ? develops a broad peak and then decreases as the temperature is increased. The anomaly in the vicinity of Tc and above its value is well accounted for in terms of interaction among the phonon?impurity, the magnon?impurity and the carrier?impurity channels of thermal conductivity. Conclusively, the temperature dependence of thermal conductivity is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between electron, magnon and phonon contributions. Numerical analysis of thermal conductivity from the present model shows similar results to those revealed from experiments.