What is commensurate and incommensurate cdw or sdw?

[sarir_sss]

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...

 

[M Quack]

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.