Since many years ago, we have achieved an excellent control over electronic currents and have created many devices that have produced a huge impact in our society and in the way we life. Transistors, for example, are part of these devices and form the nuclei of our computer, mobiles, etc. However, we are still far from achieving this control over heat flow, that is, over the phonons. The invention of devices able to manipulate heat transport could make an enormous impact, and recently, researchers from the University of California at Berkeley and Georgia State University have reported the first temperature-gated thermal rectifier devices using VO2 beams.
(Schematic operation and pictures of the novel thermal rectifiers. Picture obtained from the Nano Letters article)
The modification of the heat flux in the beams can be achieved by changing the device temperature, which controls the metallic and insulating nature of the oxide. Maximum heat suppression of 28% is observed below 340 K when mixed metallic and insulating phases coexist in the VO2 beam. Once the devices are heated above 340 K, they become completely metallic and behave as ordinary thermal conductors.
If you want to read more about the potential and recent advances in the control of phonons, I would recommend having a look to a very interesting review article appeared in Nature last year. the article highlights the new opportunities to thermally insulate buildings, reduce environmental noise, transform waste heat into electricity and develop earthquake protection. Sonic and thermal diodes, optomechanical crystals, acoustic and thermal cloaking, hypersonic phononic crystals, thermoelectrics, and thermocrystals could be the devices to create the next technological revolution in phononics.
