Thermal conductivity and specific heat of SrCu$_2$(BO$_3)_2$: A quasi-two-dimensional metal oxide compound with a spin gap

The thermal conductivity and specific heat of SrCu$_2$(BO$_3)_2$, a quasi-two-dimensional metal oxide compound with a spin gap, were studied at low temperatures. In the temperature interval $0.4<T<3.2$ K, the thermal conductivity of a single crystal sample in the $ab$ plane varies according to the power law $\kappa \propto T^{2.73}$. As the temperature increases further, a deep minimum is observed in the region of $T_{\min}\approx9.8$ K. This behavior is explained by the scattering of phonons — the major heat carriers — on the fluctuations of the spin subsystem.