Technologies to manipulate photons and electrons are pervasive in the modern world for the simple reason that they are simple to make and work with. This is not the case for heat though as the frequencies the phonons that carry thermal energy exist at very high frequencies. Researchers at MIT though have recently found a way to reduce these frequencies, and with that ability create a thermocrystal to manipulate heat within.
Phonons are the quasiparticle for all vibrations, such as sound and heat. Sonic phonons have relatively low kilohertz frequencies, which allow them to travel great distances, while thermal phonons have terahertz frequencies and persist for only nanometers. In order to manipulate thermal phonons, the researchers had to drop their frequencies down to a window between 100 and 300 gigahertz, which was accomplished with thin films of an alloy of silicon and germanium nanoparticles. This 'hypersonic heat,' as the researchers call it, is something that specially designed thermocrystal will be able to manipulate, similar to how photonic crystals control light.
The true potential of this research is not in what the MIT researchers have already done, but in what other researchers are going to do with it. This work could lead to thermal lenses, for focusing heat like light, or thermal diodes, to direct the flow of heat. Eventually thermal cloaks could be developed using similar principles as optical cloaks which rely on metamaterials.