In physics, a quasiparticle refers to a particle-like entity arising in certain systems of interacting particles. It can be thought of as a single particle moving through the system, surrounded by a cloud of other particles that are being pushed out of the way or dragged along by its motion, so that the entire entity moves along somewhat like a free particle. The quasiparticle concept is one of the most important in condensed matter physics, because it is one of the few known ways of simplifying the quantum mechanical many-body problem, and is applicable to an extremely wide range of many-body systems. The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density Physics (Greek: (phúsis), nature and (phusiké), knowledge of nature) is the branch of science concerned with the discovery and characterization of universal laws which govern matter, energy, space, and time. ... In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter. ... Fig. ... This article is about the many-body problem in quantum mechanics. ...

In the language of many-body quantum mechanics, a quasiparticle is a type of low-lying excited state of the system (a state possessing energy very close to the ground state energy) that is known as an elementary excitation. This means that most of the other low-lying excited states can be viewed as states in which multiple quasiparticles are present. It turns out that the interactions between quasiparticles become negligible at sufficiently low temperatures, in which case we can obtain a great deal of information about the system as a whole, including the flow properties and heat capacity, by investigating the properties of individual quasiparticles. Fig. ... It has been suggested that this article or section be merged with quantum state. ... In physics, the ground state of a quantum mechanical system is its lowest-energy state. ... This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... A quantum fluid can refer to a cluster of valence electrons moving together after they undergo fermionic condensation. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

Actually, most many-body systems possess two types of elementary excitations. The first type, the quasiparticles, correspond to single particles whose motions are modified by interactions with the other particles in the system. The second type of excitation corresponds to a collective motion of the system as a whole. These excitations are called collective modes, and they include phenomena such as zero sound, plasmons, and spin density waves. Zero sound is the name given by Landau to the longitudinal density vibrations in quantum fermi liquids. ... In physics, the plasmon is the quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and sound waves. ... Spin-density wave (SDW) and charge-density wave (CDW) are names for two similar low-energy ordered states of solids. ...

The idea of quasiparticles originated in Landau's theory of Fermi liquids, which was originally invented for studying liquid helium-3. For these systems a strong similarity exists between the notion of quasi-particle and dressed particles in quantum field theory. Lev Davidovich Landau (Ле́в Дави́дович Ланда́у) (January 22, 1908 – April 1, 1968) was a prominent Soviet physicist and winner of the Nobel Prize for Physics whose broad field of work included the theory of superconductivity and superfluidity, quantum electrodynamics, nuclear physics and particle physics. ... A Fermi liquid is a generic term for a quantum mechanical liquid of fermions that arises under certain physical conditions—when the temperature is sufficiently low, and when the system is translationally invariant. ... Helium-3 is a non-radioactive and light isotope of helium. ... Quantum field theory (QFT) is the quantum theory of fields. ...

The dynamics of Landau's theory is a kinetic equation of the mean-field type. A similar equation, the Vlasov Equation, is valid for a plasma in the so-called plasma approximation, in which charged particles are considered moving in the electromagnetic field collectively generated by all other particles, and hard collisions between the charged particles are neglected. When kinetic equations of the mean-field type are a valid first-order description of a system, second-order corrections determine the entropy production, and generally take the form of Boltzmann-type collision term, in which figure only "far collisions" between virtual particles. In other words, every type of mean-field kinetic equation, and in fact every Mean field theory, involves a quasi-particle concept. A many-body system with interactions is generally very difficult to solve exactly, except for extremely simple cases (Gaussian field theory, 1D Ising model. ... The Boltzmann equation, devised by Ludwig Boltzmann, describes the statistical distribution of particles in a fluid. ... A plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation. ... A many-body system with interactions is generally very difficult to solve exactly, except for extremely simple cases (Gaussian field theory, 1D Ising model. ... The Boltzmann equation describes the statistical distribution of particles in a fluid. ... A many-body system with interactions is generally very difficult to solve exactly, except for extremely simple cases (Gaussian field theory, 1D Ising model. ...

Note that the use of term quasiparticle seems to be ambiguous. Some authors use the term in order to distinguish them from real particles, others (including author of the above passage) to describe an excitation similar to a single particle excitation as opposed to a collective excitation. Both definitions mutually exclude each other as with the former definition collective excitations which are no "real" particles are considered to be quasiparticles.^{[citation needed]} Phonons are the quanta of classical sound waves and sound waves do not need the notion of atoms. Magnons are the quanta of classical spinwaves, which also do not need elementary spins. Photons inside an isolator are the quanta of classical dressed electromagnetic waves and do not need the notion of electrons for the definition of the refractive index. Plasmons are the quanta of the plasma oscillations and they only need charge density and mass density and no electrons or ions. Polarons are the quanta of the oscillating polarization in a lightly doped semiconductor and also do not need elementary charge or mass. Normals modes of vibration progression through a crystal. ... There is a place named Magnon (pronunciation: ma-nyon) in Gabon, see Magnon, Gabon A magnon is a collective excitation of the electrons spin structure in a crystal lattice. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... In physics, the plasmon is the quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and sound waves. ... In physics, plasma oscillations, often referred to as Langmuir waves or plasma waves, are periodic oscillations of charge density in conducting media such as plasmas or metals. ... In solid-state physics, a polaron is formed when a moving charge (typically an electron or a hole) in a crystal with some ionic character polarizes (by its electric field) the lattice around it. ...

Examples

• Landau quasiparticles in normal metals
• Stoner excitations in ferromagnetic metals
• Bogoliubov quasiparticles in superconductors
• The plasma approximation in plasmas

A plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation. ... A plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation. ...

This is a list of particles in particle physics, including currently known and hypothetical elementary particles, as well as the composite particles that can be built up from them. ... Normals modes of vibration progression through a crystal. ... This page is about the quasiparticle. ... In physics, the plasmon is the quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and sound waves. ... This article is in need of attention. ... In solid-state physics, a polaron is formed when a moving charge (typically an electron or a hole) in a crystal with some ionic character polarizes (by its electric field) the lattice around it. ... There is a place named Magnon (pronunciation: ma-nyon) in Gabon, see Magnon, Gabon A magnon is a collective excitation of the electrons spin structure in a crystal lattice. ...

See also

• Mean field theory

A many-body system with interactions is generally very difficult to solve exactly, except for extremely simple cases (Gaussian field theory, 1D Ising model. ...

References

• L. D. Landau, Soviet Phys. JETP. 3, 920 (1957)
• L. D. Landau, Soviet Phys. JETP. 5, 101 (1957)
• A. A. Abrikosov, L. P. Gorkov, and I. E. Dzyaloshinski, Methods of Quantum Field Theory in Statistical Physics (Prentice-Hall, New Jersey, 1963); (Dover Publications, New York, 1975)
• D. Pines, and P. Nozières, The Theory of Quantum Liquids, Volume I: Normal Fermi Liquids (W.A. Benjamin, New York, 1966); (Westview Press, Boulder, 1999)
• J. W. Negele, and H. Orland, Quantum Many-Particle Systems (Westview Press, Boulder, 1998)