In Physics, What Is a Phonon?

Benjamin Arie

A phonon is a quantity of energy found within a vibration. These are present in all objects that are actively vibrating, such as Quartz crystals. One way to consider a phonon is as a resonating particle within a wave. Just as a "photon" is a quantum particle within a light wave, a phonon is a particle within a sound wave. The term "phonon" is derived from the Greek word "phone," which means "sound or voice."

Scientist with beakers
Scientist with beakers

Russian physicist Igor Tamm is credited with first theorizing the concept of phonons. Since this concept was introduced in 1932, these quantities have been integrated into the branch of physics known as quantum mechanics. They are part of emerging and continuing research in physics. A phonon is often classified as a "quasiparticle" or "collective excitation," which generally means that it can be observed as a phenomenon but not specifically extracted as an individual physical object.

Phonons do not behave as independent particles, but instead interact with other phonons within an object. This interaction causes groups of phonons to form chains or lattice structures. One phonon is able to transfer its energy to the next one in the chain. A long lattice or group of these is able to transfer continuous energy in the form of electricity or heat.

Understanding the behavior of phonons is seen by many thermodynamic experts as the key to creating very efficient conducting or insulating materials. High conductivity is important in the fields of computer science and power storage, while extreme insulation is useful for protective materials. Research continues, as some scientists believe that useful materials may be built as a result of studying the way phonons operate and interact.

Researchers at the Massachusetts Institute of Technology (MIT) created one such material in 2010. The MIT experts combined several layers of different crystal material in a pattern designed to reflect phonons. During the experiment, the crystal material successfully stopped the movement of phonons, and caused them to reflect or "bounce" back in the opposite direction.

Phonon research may lead to the development of practical developments in the future. Some examples of inventions that are possible by manipulating phonons include protective thermal shielding for spaceships, superior insulation for freezing cold environments, and energy collectors for portable devices. Successful manipulation may lead to scientific breakthroughs similar to the rapid growth in solid-state electronics such as transistors during the second half of the 20th century.

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