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.