What is commensurate and incommensurate cdw or sdw?

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Main Question or Discussion Point

what is commensurate and incommensurate cdw or sdw?what means?
what means"sliding cdw or sdw"?
what is" coupling "in cdw or sdw?
what is" pinning" in cdw or sdw?
any help u could give would b much approciated...
 

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cdw = charge density wave = periodic displacement of ions

sdw = spin density wave = periodic arrangement of spin (antiferromagnet).

commensurate means that the periodicity is a multiple of the host crystal's unit cell.

incommensurate means the opposite.

An incommensurate cdw can be made to slide by applying a voltage.

If the displacement vector u at position r is given by u(r) = u_0 cos(k*r + phi), then sliding means that the phase phi is changing with time.

Pinning can occur at defects and may prevent sliding.

http://iopscience.iop.org/0295-5075/56/2/289/

Coupling can mean many many things....

Many times a sdw with wave vector k (period lambda) will induce a cdw with wave vektor 2k (period lambda/2) as secondary order parameter. Chromium metal is the prototype for such a system.
 

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