WikiMili The Free Encyclopedia

This article provides insufficient context for those unfamiliar with the subject.(October 2009) (Learn how and when to remove this template message) |

The **Thouless energy** is a characteristic energy scale of diffusive disordered conductors. It was first introduced by the Scottish-American physicist David J. Thouless when studying Anderson localization,^{ [1] } as a measure of the sensitivity of energy levels to a change in the boundary conditions of the system. Though being a classical quantity, it has been shown to play an important role in the quantum-mechanical treatment of disordered systems.^{ [2] }

**David James Thouless** is a British condensed-matter physicist. He is a winner of the 1990 Wolf Prize and laureate of the 2016 Nobel Prize for physics along with F. Duncan M. Haldane and J. Michael Kosterlitz for theoretical discoveries of topological phase transitions and topological phases of matter. In 2016, Thouless was reported to be suffering from dementia.

In condensed matter physics, **Anderson localization** is the absence of diffusion of waves in a *disordered* medium. This phenomenon is named after the American physicist P. W. Anderson, who was the first to suggest that electron localization is possible in a lattice potential, provided that the degree of randomness (disorder) in the lattice is sufficiently large, as can be realized for example in a semiconductor with impurities or defects.

It is defined by

- ,

where *D* is the diffusion constant and *L* the size of the system, and thereby inversely proportional to the diffusion time

through the system.

In quantum field theory, the **Casimir effect** and the **Casimir–Polder force** are physical forces arising from a quantized field. They are named after the Dutch physicist Hendrik Casimir who predicted them in 1948.

The **quantum Hall effect** is a quantum-mechanical version of the Hall effect, observed in two-dimensional electron systems subjected to low temperatures and strong magnetic fields, in which the Hall conductance *σ* undergoes quantum Hall transitions to take on the quantized values

In condensed matter physics, a **spin glass** is a disordered magnet, where the magnetic spins of the component atoms are not aligned in a regular pattern. The term "glass" comes from an analogy between the *magnetic* disorder in a spin glass and the *positional* disorder of a conventional, chemical glass, e.g., a window glass. In window glass or any amorphous solid the atomic bond structure is highly irregular; in contrast, a crystal has a uniform pattern of atomic bonds. In ferromagnetic solid, magnetic spins all align in the same direction; this would be analogous to a crystal.

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 first proposed by Lev Landau in 1933 to describe an electron moving in a dielectric crystal where the atoms move 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.

The **classical XY model** (sometimes also called **classical rotor****model** or **O model**) is a lattice model of statistical mechanics. It is the special case of the *n*-vector model for *n* = 2.

**Jellium**, also known as the **uniform electron gas** (**UEG**) or **homogeneous electron gas** (**HEG**), is a quantum mechanical model of interacting electrons in a solid where the positive charges are assumed to be uniformly distributed in space whence the electron density is a uniform quantity as well in space. This model allows one to focus on the effects in solids that occur due to the quantum nature of electrons and their mutual repulsive interactions without explicit introduction of the atomic lattice and structure making up a real material. Jellium is often used in solid-state physics as a simple model of delocalized electrons in a metal, where it can qualitatively reproduce features of real metals such as screening, plasmons, Wigner crystallization and Friedel oscillations.

The **Berezinskii–Kosterlitz–Thouless transition** is a phase transition in the two-dimensional (2-D) XY model. It is a transition from bound vortex-antivortex pairs at low temperatures to unpaired vortices and anti-vortices at some critical temperature. The transition is named for condensed matter physicists Vadim Berezinskii, John M. Kosterlitz and David J. Thouless. BKT transitions can be found in several 2-D systems in condensed matter physics that are approximated by the XY model, including Josephson junction arrays and thin disordered superconducting granular films. More recently, the term has been applied by the 2-D superconductor insulator transition community to the pinning of Cooper pairs in the insulating regime, due to similarities with the original vortex BKT transition.

**Fluorescence correlation spectroscopy** (**FCS**) is a correlation analysis of fluctuation of the fluorescence intensity. The analysis provides parameters of the physics under the fluctuations. One of the interesting applications of this is an analysis of the concentration fluctuations of fluorescent particles (molecules) in solution. In this application, the fluorescence emitted from a very tiny space in solution containing a small number of fluorescent particles (molecules) is observed. The fluorescence intensity is fluctuating due to Brownian motion of the particles. In other words, the number of the particles in the sub-space defined by the optical system is randomly changing around the average number. The analysis gives the average number of fluorescent particles and average diffusion time, when the particle is passing through the space. Eventually, both the concentration and size of the particle (molecule) are determined. Both parameters are important in biochemical research, biophysics, and chemistry.

In statistical physics of disordered systems, the **random energy model** is a toy model of a system with quenched disorder. It concerns the statistics of a system of particles, such that the number of possible states for the systems grow as , while the energy of such states is a Gaussian stochastic variable. The model has an exact solution. Its simplicity makes this model suitable for pedagogical introduction of concepts like quenched disorder and replica symmetry.

**Reaction–diffusion systems** are mathematical models which correspond to several physical phenomena: the most common is the change in space and time of the concentration of one or more chemical substances: local chemical reactions in which the substances are transformed into each other, and diffusion which causes the substances to spread out over a surface in space.

In solid-state physics, **heavy fermion materials** are a specific type of intermetallic compound, containing elements with 4f or 5f electrons in unfilled electron bands. Electrons are one type of fermion, and when they are found in such materials, they are sometimes referred to as **heavy electrons**. Heavy fermion materials have a low-temperature specific heat whose linear term is up to 1000 times larger than the value expected from the free electron model. The properties of the heavy fermion compounds often derive from the partly filled f-orbitals of rare-earth or actinide ions, which behave like localized magnetic moments. The name "heavy fermion" comes from the fact that the fermion behaves as if it has an effective mass greater than its rest mass. In the case of electrons, below a characteristic temperature (typically 10 K), the conduction electrons in these metallic compounds behave as if they had an effective mass up to 1000 times the free particle mass. This large effective mass is also reflected in a large contribution to the resistivity from electron-electron scattering via the Kadowaki–Woods ratio. Heavy fermion behavior has been found in a broad variety of states including metallic, superconducting, insulating and magnetic states. Characteristic examples are CeCu_{6}, CeAl_{3}, CeCu_{2}Si_{2}, YbAl_{3}, UBe_{13} and UPt_{3}.

First introduced by M. Pollak, the **Coulomb gap** is a soft gap in the Single-Particle Density of States (DOS) of a system of interacting localized electrons. Due to the long-range Coulomb interactions, the single-particle DOS vanishes at the chemical potential, at low enough temperatures, such that thermal excitations do not wash out the gap.

**Diffusion** is the net movement of molecules or atoms from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in chemical potential of the diffusing species.

In condensed matter physics, **biexcitons** are created from two free excitons.

The **Holstein–Herring method**, also called the **surface Integral method**, also called **Smirnov's method** is an effective means of getting the exchange energy splittings of asymptotically degenerate energy states in molecular systems. Although the exchange energy becomes elusive at large internuclear systems, it is of prominent importance in theories of molecular binding and magnetism. This splitting results from the symmetry under exchange of identical nuclei.

The **kicked rotator**, also spelled as **kicked rotor**, is a prototype model for chaos and quantum chaos studies. It describes a particle that is constrained to move on a ring. The particle is kicked periodically by an homogeneous field. The model is described by the Hamiltonian

**Thomas C. Spencer** is an American mathematical physicist, known in particular for important contributions to constructive quantum field theory, statistical mechanics, and spectral theory of random operators. He earned his doctorate in 1972 from New York University with a dissertation entitled *Perturbation of the Po2 Quantum Field Hamiltonian* written under the direction of James Glimm. Since 1986, he has been professor of mathematics at the Institute for Advanced Study. He is a member of the United States National Academy of Sciences, and the recipient of the Dannie Heineman Prize for Mathematical Physics.

A unified model for *Diffusion Localization and Dissipation* (DLD), optionally termed *Diffusion with Local Dissipation*, has been introduced for the study of *Quantal Brownian Motion* (QBM) in dynamical disorder. It can be regarded as a generalization of the familiar Caldeira-Leggett_model.

In quantum probability, the **Belavkin equation**, also known as **Belavkin-Schrödinger equation**, **quantum filtering equation**, **stochastic master equation**, is a quantum stochastic differential equation describing the dynamics of a quantum system undergoing observation in continuous time. It was derived and henceforth studied by Viacheslav Belavkin in 1988.

- ↑ J. T. Edwards and D. J. Thouless, "Numerical studies of localization in disordered systems,"
*J. Phys. C: Solid State Phys.***5**, 807 (1972), doi : 10.1088/0022-3719/5/8/007. - ↑ A. Altland, Y. Gefen, and G. Montambaux, "What is the Thouless Energy for Ballistic Systems?",
*Physical Review Letters***76**, 1130 (1996), doi : 10.1103/PhysRevLett.76.1130.

This physics-related article is a stub. You can help Wikipedia by expanding it. |

This page is based on this Wikipedia article

Text is available under the CC BY-SA 4.0 license; additional terms may apply.

Images, videos and audio are available under their respective licenses.

Text is available under the CC BY-SA 4.0 license; additional terms may apply.

Images, videos and audio are available under their respective licenses.