A charge density wave (CDW) is a periodic modulation of the electronic charge density - a standing wave in the electronic wave functions created by combining electron states moving in opposite directions. Several quasi-2-D systems, including layered transition metal dichalcogenides,[5] undergo Peierls transitions to form quasi-2-D CDWs. These result from multiple nesting wavevectors coupling different flat regions of the Fermi surface. The charge modulation can either form a honeycomb lattice with hexagonal symmetry or a checkerboard pattern. In 2012, evidence for competing, incipient CDW phases were reported for layered cuprate high-temperature superconductors such as YBCO. Peierls transition : A Peierls transition or Peierls distortion is a distortion of the periodic lattice of a one-dimensional crystal. Atomic positions oscillate so that the perfect order of the 1-D crystal is broken. The theory was based on the idea that pairing of electrons in the BCS theory of superconductivity could be mediated by interactions of conducting electrons in one chain with nonconducting electrons in some side chains. (By contrast, electron pairing is mediated by phonons, or vibrating ions, in the BCS theory of conventional superconductors.) Anderson localization : In condensed matter physics, Anderson localization, also known as strong 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 one to suggest the possibility of electron localization inside a semiconductor, provided that the degree of randomness of the impurities or defects is sufficiently large. Quantum models of CDW transport : Following Richard Feynman in The Feynman Lectures on Physics, Vol. III, Ch. 21, their time-evolution is described using the Schrödinger equation as an emergent classical equation. The narrow-band noise and related phenomena result from the periodic buildup of electrostatic charging energy and thus do not depend on the detailed shape of the washboard pinning potential. Both a soliton pair-creation threshold and a higher classical depinning field emerge from the model, which views the CDW as a sticky quantum fluid or deformable quantum solid with dislocations, a concept discussed by Philip Warren Anderson. file.scirp.org/Html/2-1220069_46444.htm
Posted on: Wed, 10 Dec 2014 01:22:30 +0000