# Cdw sdw2

1. Jun 14, 2012

### sarir_sss

why cdw occurs at low dimensional solids with anisotropic fermi surfaces that have prominent nesting vectors?/
what it means : cdws are also common at the surface of solids???????where they are more commonly called surface reconstruction or dimerization .
PLZ tell me about two dimensional Fermi surface? thanks so muchhhhhhhhhh

Last edited: Jun 14, 2012
2. Jun 15, 2012

### M Quack

A surface reconstruction is the re-arrangement of the last or few last layers of atoms at the surface of a single crystal. In general this is due to the missing neighbors at the surface.

http://en.wikipedia.org/wiki/Surface_reconstruction

I guess you could view surface reconstructions as special cases of CDW (after all atoms get displaced), but I suspect that the underlying physics is quite different. Surface reconstructions tend to be commensurate.

Note that a "conventional" CDW is a bulk phenomenom, and that the CDW extends perpendicular to the propagation wave vector.

Nesting occurs when sections of the Fermi surface are parallel to each other, i.e. when there is a reciprocal space vector that can transfer an electron from one part of the Fermi surface to another over some non-zero area of the Fermi surface. This creates an instability in the electronic system that can result in the formation of a modulated state such as CDW or SDW. The modulation wave vector is the reciprocal space vector that links the two parts of the Fermi surface.

Last edited: Jun 15, 2012