Tunneling across a tiny gap

Conduction and thermal radiation are two ways in which heat is transferred from one object to another: Conduction is the process by which heat flows between objects in physical, such as a pot of tea on a hot stove, while thermal radiation describes heat flow across large distances, such as heat emitted by the sun. These two fundamental heat-transfer processes explain how energy moves across microscopic and macroscopic distances. But it's been difficult for researchers to ascertain how heat flows across intermediate gaps. Now researchers at MIT, the University of Oklahoma, and Rutgers University have developed a model that explains how heat flows between objects separated by gaps of less than a nanometer. The team has developed a unified framework that calculates heat transport at finite gaps, and has shown that heat flow at sub-nanometer distances occurs not via radiation or conduction, but through "phonon tunneling." Phonons represent units of energy produced by vibrating atoms in a crystal lattice. For example, a single crystal of table salt contains atoms of sodium and chloride, arranged in a lattice pattern. Together, the atoms vibrate, creating mechanical waves that can transport heat across the lattice.