Introducing the phoniton

By Hamish Johnston

Condensed-matter physicists have their own particle zoo – a menagerie filled with familiar and exotic quasiparticles including old favourites like holes and phonons, and newer additions such as surface plasma polaritons. Quasiparticles are excitations in a solid that behave like tiny particles and obey quantum mechanics. A phonon for example, is a quantized sound wave that propagates through a crystal.

Now Charles Tahan and colleagues at the Laboratory for Physical Sciences just outside Washington, DC have shown that the interaction between phonons and electronic excitations in certain semiconductors can be described in terms of a brand new quasiparticle called the phoniton.

The team studied phonitons in silicon doped with phosphorous. As a phonon moves through the material it stretches and squeezes the crystalline lattice such than an electron associated with a phosphorous atom absorbs the phonon’s energy and is promoted into a higher energy level. This electron then decays back to its original energy, re-emitting the phonon, which can be absorbed and re-emitted at another phosphorous atom. The propagation of this phonon/excitation hybrid through the lattice can be described as a quasiparticle they have called the phoniton.

So what use could a phoniton be? Because they combine the electronic and mechanical properties of a material, they could be put to work in mechanical sensors that detect vibration, strain or other movement. Looking further into the future, they could also find use in quantum computers that use phonons to store and process information.

You can read more about phonitons in Phys. Rev. Lett. 107 253502.

If you don’t have access to APS journals, you can read a preprint of the article here. Before you click through to the PDF, look at the comments where is says “Changed ‘phononitons’ to ‘phoniton’ by negotiation with PRL editors…”. I have to agree with the editors, phononitons is a real mouthful!