Exposing the hidden influence of selection rules on phonon-phonon scattering by pressure and temperature tuning*

Selection rules act to restrict intrinsic anharmonic interactions between phonons in all crystals. Yet their influence on phonon propagation is often hidden and so hard to interrogate experimentally. Using ab initio calculations, we show that the hidden influence of selection rules on three-phonon scattering can be exposed through anomalous signatures in the pressure (P) and temperature (T) dependence of the thermal conductivities, k, of certain compounds. Boron phosphide reveals such underlying behavior through an exceptionally sharp initial rise in k with increasing P, which may be the steepest of any material, and also a peak and decrease in k at high P. These features are in stark contrast to the measured behavior for many solids, and occur at experimentally accessible conditions.