Low-temperature magneto-thermal conductivity of the helimagnet Cu$_2$OSeO$_3$*

We report measurements of thermal conductivity ($\kappa$) in the range $0.6\ {\rm K}\leq T\leq 200$~K for single crystals of the helimagnetic insulator Cu$_2$OSeO$_3$. A maximum in $\kappa$ near $T=8$~K with $\kappa_{max}\sim 300$~W/mK implies a very high lattice quality for an oxide. The magneto-thermal conductivity at $T\leq 10$~K and influence of spin-reorientation transitions associated with low-$T$ magnetic phases will be discussed for different orientations of the magnetic field relative to the crystallographic and heat flow directions.