Abstract
Energy- and momentum-conserving phonon-phonon interactions can give rise to a reversal in the net energy flow per unit area, U, in crystals having sufficient elastic anisotropy. This results because the direction of phonon momentum is, in general, not parallel to the energy-flow vector in elastically anisotropic crystals. Conditions for energy-flow reversal (EFR) about a 〈100〉 or 〈110〉 reference axis have been calculated for cubic crystals when the wave vectors of the three interacting phonons are constrained to a {100} or [110} symmetry plane. Six interactions qualify for EFR under these conditions when the elastic anisotropy factor Ag1; two qualify when Al1. More than a dozen cubic crystals are shown to satisfy conditions for EFR in one or more of these interactions. A proposed room-temperature experiment is described to demonstrate EFR in tetragonal paratellurite.
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