Thermal conductivity and specific heat of the spin-ice compound Dy_2Ti_2O_7: Experimental evidence for monopole heat transport

摘要

Elementary excitations in the spin-ice compound Dy_2Ti_2O_7 can be described as magnetic monopoles propagating independently within the pyrochlore lattice formed by magnetic Dy ions. We studied the magnetic-field dependence of the thermal conductivity κ(B) for B || [001] and observe clear evidence for magnetic heat transport originating from the monopole excitations. The magnetic contribution κ_(mag) is strongly field dependent and correlates with the magnetization M(B). The diffusion coefficient obtained from the ratio of κ_(mag) and the magnetic specific heat is strongly enhanced below 1 K, indicating a high mobility of the monopole excitations in the spin-ice state.