The first controlled collisions of quasiparticles within a solid have been achieved by an international group of physicists. By firing a laser pulse at a semiconductor, the group created "excitons" – electron–hole pairs bound to each other via electrostatic attraction. This new experimental technique could resolve the dynamics of the collision to about two femtoseconds. The researchers say that, apart from improving our understanding of the fundamental physics of excitons, the technique opens the door to studying the fast dynamics of quasiparticle interactions in solids. It could even be used to design semiconductor devices in the future.


PW quasiparticles


Quasiparticles such as the exciton are configurations of particles that have distinctive collective behaviour. It's analogous to a bubble in water, says Mackillo Kira at Philipps-Universität Marburg in Germany. When describing bubble behaviour, it's easier to treat the bubble as a single particle "rather than considering all of the water molecules at once", he says. Similarly, quasiparticles are a more illuminating way of studying the bulk behaviour of semiconductors and other solids compared with individual electrons. Quasiparticle interactions are often used to explain material properties such as resistivity, heat capacity and superconductivity.