Explanation

The concept of quasi particle is one of the methods introduced to simplify many body problems. It calls the stable excitation with certain energy and momentum in the system, and the energy and momentum meet a certain dispersion law as quasi particle. It simplifies the system with strong interaction into a system composed of quasi particle. For example, the solid is regarded as a phonon system (phonon gas), the free electrons in the metal are regarded as an electronic system (electronic gas), and the balanced radiation field is regarded as a photon system (photonic gas). quasi particle is similar to an entity in an interacting particle system. When a particle in the entity passes through the system and moves in a certain direction, other particle clouds around the particle flash away from the original motion track for the interaction between them, or are "dragged to move in a certain direction". From a macro perspective, this system is like a free moving whole. That is, a "quasi particle". In physics, quasi particle or collective excitation refers to the collective excitation of quasi particles in interacting multi body systems. quasi particle can also be called meta excitation. Landau's Fermi liquid theory points out that the energy level of the interacting system can be classified according to the same quantum number as the non interacting particles. The interacting particle state is called a quasi particle state or a meta excited state.

Classification