Charge & spin density waves

Charge density waves (CDWs) are broken symmetry states of mostly strongly anisotropic quasi-one dimensional metals (see [1] for a review). As a result of a Peierls instability their ground state is a coherent superposition of electron-hole pairs which results in a periodic spatial modulation of the charge density. For a partially filled electron band, its period is in general incommensurate with the underlying lattice. In perfectly clean crystals there is then a gapless excitation branch, giving rise to an infinite conductivity at zero frequency.
The coupling of the CDW to impurities and the underlying lattice will distort its modulation and leads to a variety of interesting effects. Recently we found a new type of disorder driven roughening transition between two phases which are either dominated by impurity or disorder pinning [2].
We were also interested in the anorganic material CuGeO₃, which shows a Spin-Peierls transition and an commensurate-incommensurate transition for increasing magnetic field at low temperatures [3].
A very similar picture is found for other incommensurate structures like spin density waves in anisotropic metals, mass density waves in superionic conductors, polarization density waves in incommensurate ferroelectrics etc.. More recently, the ground state of a two-dimensional system of interacting electrons in intermediate magnetic fields has been proposed to be a CDW. We have examined this system in the framework of a Chern-Simons-Ginzburg -Landau theory [4].