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Polaron
A polaron is a quasiparticle used in condensed matter physics to understand the interactions between electrons and atoms in a solid material. The polaron concept was proposed by Lev Landau in 1933 and Solomon Pekar in 1946 to describe an electron moving in a dielectric crystal where the ions, atoms displace from their equilibrium positions to effectively screen the charge of an electron, known as a phonon cloud. This lowers the electron mobility and increases the electron's effective mass (solid-state physics), effective mass. The general concept of a polaron has been extended to describe other interactions between the electrons and ions in metals that result in a bound state, or a lowering of energy compared to the non-interacting system. Major theoretical work has focused on solving Herbert Fröhlich, Fröhlich and Holstein hamiltonian (quantum mechanics), Hamiltonians. This is still an active field of research to find exact numerical solutions to the case of one or two electro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solomon Pekar
Solomon Isakovych Pekar (; 16 March 1917 – 8 July 1985) was a Soviet theoretical physicist, born in Kyiv, Ukraine. He was a full Member of the Ukrainian Academy of Sciences and is known for his fundamental contributions to condensed matter physics, especially for introducing and advancing the concept of polaron as a charge carrier in solids. Career In 1941 Pekar submitted his Candidate of Science thesis on nonlinear theory of semiconductor rectifiers for which he was awarded Doctor of Science Degree, this work was strongly approved by Lev Landau. In 1946, Pekar developed a concept of a polaron and coined this term. The model developed in this paper is macroscopic and based on electrostatic coupling of an electron to polar optical phonons. This coupling results in dressing of the electron by a cloud of virtual phonons and renormalization of its energy spectrum. In the strong coupling limit, polaron binding energy was found by Pekar, and its effective mass is described by the La ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Herbert Fröhlich
Herbert Fröhlich (9 December 1905 – 23 January 1991) FRS was a German-born British physicist. Personal life Fröhlich was born on 9 December 1905 in Rexingen, Baden-Württemberg. He was the son of Fanny Frida (née Schwarz) and Jakob Julius Fröhlich, members of an old-established Jewish family, and the brother of Albrecht Fröhlich, a mathematician who was elected Fellow of the Royal Society in 1976. Career In 1927, Fröhlich entered Ludwig-Maximilians University in Munich to study physics, and received his doctorate under Arnold Sommerfeld in 1930. His first position was as Privatdozent at the University of Freiburg. Due to rising anti-Semitism and the Deutsche Physik movement under Adolf Hitler, and at the invitation of Yakov Frenkel, Fröhlich went to the Soviet Union, in 1933, to work at the Ioffe Physico-Technical Institute in Leningrad. During the Great Purge following the murder of Sergei Kirov, he fled to England in 1935. Except for a short visit to the Nether ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lev Landau
Lev Davidovich Landau (; 22 January 1908 – 1 April 1968) was a Soviet physicist who made fundamental contributions to many areas of theoretical physics. He was considered as one of the last scientists who were universally well-versed and made seminal contributions to all branches of physics. He is credited with laying the foundations of twentieth century condensed matter physics, and is also considered arguably the greatest Soviet theoretical physicist. His accomplishments include the independent co-discovery of the density matrix method in quantum mechanics (alongside John von Neumann), the quantum mechanical theory of diamagnetism, the theory of superfluidity, the theory of second-order phase transitions, invention of order parameter technique, the Ginzburg–Landau theory of superconductivity, the theory of Fermi liquids, the explanation of Landau damping in plasma physics, the Landau pole in quantum electrodynamics, the two-component theory of neutrinos, and Landau's ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polariton
In physics, polaritons are bosonic quasiparticles resulting from strong coupling of electromagnetic waves (photon) with an electric or magnetic dipole-carrying excitation (state) of solid or liquid matter (such as a phonon, plasmon, or an exciton). Polaritons describe the crossing of the dispersion of light with any interacting resonance. They are an expression of level repulsion (quantum phenomenon), also known as the avoided crossing principle. To this extent polaritons can be thought of as the new normal modes of a given material or structure arising from the strong coupling of the bare modes, which are the photon and the dipolar oscillation. Bosonic quasiparticles are distinct from polarons (fermionic quasiparticle), which is an electron plus an attached phonon cloud. Polaritons violate the weak coupling limit and the associated photons do not propagate freely in crystals. Instead, propagation speed depends strongly on the frequency of the photon. Significant exper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Solar Cells
An organic solar cell (OSC) or plastic solar cell is a type of photovoltaic that uses organic electronics, a branch of electronics that deals with conductive organic polymers or small organic molecules, for light absorption and charge transport to produce electricity from sunlight by the photovoltaic effect. Most organic photovoltaic cells are polymer solar cells. The molecules used in organic solar cells are solution-processable at high throughput and are cheap, resulting in low production costs to fabricate a large volume. Combined with the flexibility of organic molecules, organic solar cells are potentially cost-effective for photovoltaic applications. Molecular engineering (''e.g.,'' changing the length and functional group of polymers) can change the band gap, allowing for electronic tunability. The optical absorption coefficient of organic molecules is high, so a large amount of light can be absorbed with a small amount of materials, usually on the order of hundreds of nan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quasiparticle
In condensed matter physics, a quasiparticle is a concept used to describe a collective behavior of a group of particles that can be treated as if they were a single particle. Formally, quasiparticles and collective excitations are closely related phenomena that arise when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in vacuum. For example, as an electron travels through a semiconductor, its motion is disturbed in a complex way by its interactions with other electrons and with atomic nuclei. The electron behaves as though it has a different effective mass travelling unperturbed in vacuum. Such an electron is called an ''electron quasiparticle''. In another example, the aggregate motion of electrons in the valence band of a semiconductor or a hole band in a metal behave as though the material instead contained positively charged quasiparticles called ''electron holes''. Other quasiparticles or collective ex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bosonic
In particle physics, a boson ( ) is a subatomic particle whose spin quantum number has an integer value (0, 1, 2, ...). Bosons form one of the two fundamental classes of subatomic particle, the other being fermions, which have half odd-integer spin (1/2, 3/2, 5/2, ...). Every observed subatomic particle is either a boson or a fermion. Paul Dirac coined the name ''boson'' to commemorate the contribution of Satyendra Nath Bose, an Indian physicist. Some bosons are elementary particles occupying a special role in particle physics, distinct from the role of fermions (which are sometimes described as the constituents of "ordinary matter"). Certain elementary bosons (e.g. gluons) act as force carriers, which give rise to forces between other particles, while one (the Higgs boson) contributes to the phenomenon of mass. Other bosons, such as mesons, are composite particles made up of smaller constituents. Outside the realm of particle physics, multiple identical composite bosons behav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fermionic
In particle physics, a fermion is a subatomic particle that follows Fermi–Dirac statistics. Fermions have a half-integer spin (spin , spin , etc.) and obey the Pauli exclusion principle. These particles include all quarks and leptons and all composite particles made of an odd number of these, such as all baryons and many atoms and nuclei. Fermions differ from bosons, which obey Bose–Einstein statistics. Some fermions are elementary particles (such as electrons), and some are composite particles (such as protons). For example, according to the spin-statistics theorem in relativistic quantum field theory, particles with integer spin are bosons. In contrast, particles with half-integer spin are fermions. In addition to the spin characteristic, fermions have another specific property: they possess conserved baryon or lepton quantum numbers. Therefore, what is usually referred to as the spin-statistics relation is, in fact, a spin statistics-quantum number relation. As a cons ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
F-center
An F-center or color center or Farbe center (from the original German ''Farbzentrum'', where ''Farbe'' means ''color'' and ''zentrum'' means ''center'') is a type of crystallographic defect in which an anionic Vacancy defect, vacancy in a crystal lattice is occupied by one or more unpaired electrons. Electrons in such a vacancy in a crystal lattice tend to absorb light in the visible spectrum such that a material that is usually Transparency (optics), transparent becomes colored. The greater the number of F centers, the more intense the color of the compound. F centers are a type of color center. This is used to identify many compounds, especially zinc oxide (yellow). History Before the discovery of point defects it was already known that some crystals can be discolored using various methods. In 1830 T.J. Pearsall discovered that fluorspar could be discolored using violet light. Thirty years later similar results were achieved by melting crystals together with a specific metal. In ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crystal Lattice
In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystal, crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat along the principal directions of Three-dimensional space (mathematics), three-dimensional space in matter. The smallest group of particles in a material that constitutes this repeating pattern is the unit cell of the structure. The unit cell completely reflects the symmetry and structure of the entire crystal, which is built up by repetitive Translation (geometry), translation of the unit cell along its principal axes. The translation vectors define the nodes of the Bravais lattice. The lengths of principal axes/edges, of the unit cell and angles between them are lattice constants, also called ''lattice parameters'' or ''cell parameters''. The symmetry properties of a crystal are described by the concept of space groups. All possi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
