Piezoelectricity and ballistic heat flow

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Abstract
We have examined the influence of piezoelectricity on the propagation of ballistic heat pulses in a lithium niobate crystal cooled to low temperatures. The phonon-imaging method reveals a ballistic flux pattern which cannot be explained simply in terms of the constant-field elastic tensor. The effect of introducing piezoelectrically stiffened elastic constants into the phonon-focusing calculation is striking. For example, caustics are introduced into the flux pattern for fast transverse phonons, in good agreement with the observations.