Enlargement of band gaps on thermal wave crystals by using heterostructures

Thermal wave crystals are periodic structures that support temperature wave oscillations. In these lattices, band gaps exist for heat flow due to interference phenomena. In this work, we demonstrate how heterostructures—a stack of two different lattices—can be used to increase band gaps. We investigate two distinct periodic structures. The first is a biological composite made up of stratum-like and dermal-like materials where we have found a band gap enlargement from 1.93 to 10.08 Hz. The second is composed of two semiconductors, silicon (Si) and germanium (Ge), where we have designed a heterostructure with a band gap ranging 0.096 to 0.17 Thz. The design of heterostructures to increase band gaps is especially useful when there is a low contrast of material parameters, as is the case of semiconductors.