Heat transport of the spin-ice materials Ho_2Ti_2O_7 and Dy_2Ti_2O_7

摘要

The elementary excitations of the spin-ice materials Ho_2Ti_2O_7 and Dy_2Ti_2O_7 in zero field can be described as independent magnetic monopoles. We investigate the influence of these exotic excitations on the heat transport by measuring the magnetic-field dependent thermal conductivity k. Additional measurements on the highly dilute reference compounds HoYTi_2O_7 and DyYTi_2O_7 enable us to separate κ into a sum of phononic (κ_(ph)) and magnetic (κ_(mag)) contributions. For both spin-ice materials, we derive significant zero-field contributions κ_(mag), which are rapidly suppressed in finite magnetic fields. Moreover, κ_(mag) sensitively depends on the scattering of phonons by magnetic excitations, which is rather different for the Ho- and the Dy-based materials and, as a further consequence, the respective magnetic-field dependent changes κ_(ph)(B) are even of opposite signs.