Strong Damping of Phononic Heat Current by Magnetic Excitations inSrCu2(BO3)2

Abstract
Measurements of the thermal conductivity as a function of temperature and magnetic field in the 2D dimer spin system SrCu2(BO3)2 are presented. In zero magnetic field the thermal conductivity along and perpendicular to the magnetic planes shows a pronounced double-peak structure as a function of temperature. The low-temperature maximum is drastically suppressed with increasing magnetic field. Our quantitative analysis reveals that the heat current is due to phonons and that the double-peak structure arises from pronounced resonant scattering of phonons by magnetic excitations.