Heat transport in the frustrated spin-ladder compound, BiCu$_2$PO$_6$*

We report measurements of thermal conductivity ($\kappa$) in the range $0.4\ {\rm K}\leq T\leq 300$~K for single-crystal BiCu$_2$PO$_6$, a recently discovered\footnote{B. Koteswararao {\it et al.}, Phys. Rev. B {\bf 76}, 052402 (2007).} frustrated 2-leg spin-ladder compound. For heat flow both along and transverse to the spin ladders, $\kappa$ exhibits a broad maximum near 60 K, coinciding with a similar maximum reported in the magnetic susceptibility, and consistent with resonant phonon scattering from spin excitations with an energy scale 40-60 K. Anisotropy in $\kappa$, evidence for a spin contribution at low temperatures, and the influence of magnetic field will be discussed.