High Temperature Magnon Thermal Conductivity in Cuprates

Some cuprates have high thermal conductivities due to the strong exchange interaction, which leads to high magnon group velocities. However, little is known about the behavior of the magnons in the cuprates above room temperature. In our study, we use the time-domain thermoreflectance (TDTR) to investigate the high magnon thermal conductivities of different cuprates at temperatures from 75 K to 600 K. Each of the cuprates studied has a different arrangement of spin-spin coupling: SrCuO₂ (a spin-chain), CaCu₂O₃ (a buckled spin ladder/pseudo-two-leg-ladder), and La₂CuO₄ (a two-dimensional square lattice). CaCu₂O₃ and La₂CuO₄ have peaks in their thermal conductivities near room temperature (~300K), but the temperature dependence of thermal conductivity differs at higher temperatures. While SrCuO₂ has a monotonically decreasing thermal conductivity with temperature, its thermal conductivity at higher temperatures are still at least two times higher than the other two cuprates. Our work seeks to explain how different arrangements of spin-spin coupling, the spin-phonon interaction, and magnetic dispersion lead to the different behaviors of thermal conductivity in these cuprates.