Thermal conductivity of the two-dimensional spin-gap system SrCu2(BO3)(2) in magnetic fields

We hal e measured the thermal conductivity of tile two-dimensional spin-gap system SrCu2(BO3)(2) single crystal in magnetic fields up to 14T. In zero field, both the in-plane and out-of-plane thermal conductivities exhibit an omalous enhancement at low temperatures below similar to 11K. The enhanceme nt is suppressed with increasing magnetic field. The enhancement in zero fi eld is attributed to the increase of the thermal conductivity due to phonon s, which is caused by the suppression of the phonon-magnon scattering owing to the spin-gap formation. The suppression of the enhancement by the appli cation of magnetic field is explained by the reduction of the spin gap.