Charge density wave
A charge density wave (English charge density wave, CDW ) is a ground state in certain quasi- one-dimensional conductors, which is characterized by collective leadership qualities. It has been since the 1930s discussed theoretically and demonstrated experimentally in the 1970s.
Description
The underlying mechanism first investigated Rudolf Peierls in 1930 in the one-dimensional case. CDW when both the density of the conduction electrons and the position of the lattice atoms periodically modulated at a wavelength ( the Fermi wave vector), corresponding to a wave vector. The lattice and electron modes are coupled. The amplitude of the displacements is relatively small ( less than one percent of the distance between the lattice atoms, and also in the density of the conduction electrons few percent). In CDW formed as Peierls showed a band gap in from the so-called Peirls gap through which the energy of the conduction electrons is lowered near the Fermi surface, which compensates the energy required for the associated lattice vibration at low temperatures in one-dimensional systems. CDW -mode in these systems is therefore the preferred primary mode if the temperature is low enough ( at the higher temperature, the metal state is stable due to thermal excitations). There is a so-called Peierls transition from the metallic state to the CDW state, a second-order phase transition.
CDW show when an electric field of collective charge transport, but it depends on the underlying lattice. Usually the wave vectors of the CDW is incommensurate with the lattice periods, and the CDW is " nailed " in impurities. Only at a certain applied electric field strength occurs on collective leadership ( the CDW " slides " then the impurities ). The forwarding behavior is strongly nonlinear. CDW materials are characterized by very large values of the dielectric constant. In the metallic state they are strongly anisotropic. They show a rich dynamical behavior ( such as hysteresis and memory effects, coherent ac components in the CDW current, mode locking of the CDW current at an applied alternating current Shapiro steps in the current-voltage characteristic), mainly due to the interaction with are the CDW retentive impurities due.
CDW were first discovered in 1977 by Nai- Phuan Ong and Pierre Monceau due to their unusual conduction properties in niobium triselenide ( NbSe3 ) and since then. In a number of other inorganic and organic materials, which are characterized at the atomic level usually by one-dimensional ( chain-like ) structures The transition takes place at NbSe3 at 145 Kelvin, but can also occur above room temperature, for example at Niobtrisulfid ( NbS3 ) at 340 Kelvin. It is usually 50 to 200 Kelvin in the area.
CDW are related to spin density waves, which can be regarded from two CDW each of opposite spin as.
CDW theorists serve as an exemplary object of study of the interaction of a collective excitation with randomly distributed impurities. A commonly used model is the FLR model for CDW, named after Hidetoshi Fukuyama, Patrick A. Lee and T. Maurice Rice.