Spin density wave

Fundamentally SDWs and CDWs involve the development of a superstructure in the form of a periodic modulation in the density of the electronic spins and charges with a characteristic spatial frequency

form density waves while others choose a superconducting or magnetic ground state at low temperatures, because of the existence of nesting vectors in the materials' Fermi surfaces.

The concept of a nesting vector is illustrated in the Figure for the famous case of chromium, which transitions from a paramagnetic to SDW state at a Néel temperature of 311 K. Cr is a body-centered cubic metal whose Fermi surface features many parallel boundaries between electron pockets centered at

and hole pockets at H. These large parallel regions can be spanned by the nesting wavevector

The theory of CDWs was first put forth by Rudolf Peierls of Oxford University, who was trying to explain superconductivity.

Many low-dimensional solids have anisotropic Fermi surfaces that have prominent nesting vectors.

Well-known examples include layered materials like NbSe3,[1] TaSe2[2] and K0.3MoO3 (a Chevrel phase)[3] and quasi-1D organic conductors like TMTSF or TTF-TCNQ.

[5] More recently, monatomic chains of Co on a metallic substrate were experimentally shown to exhibit a CDW instability and was attributed to ferromagnetic correlations.

Typically the sliding will not begin until a "depinning" threshold field is exceeded where the wave can escape from a potential well caused by a defect.

The hysteretic motion of density waves is therefore not unlike that of dislocations or magnetic domains.