Classification of charge density waves based on their nature

Physics Professors Ward Plummer and Jiandi Zhang in collaboration with their colleagues from the Institute of Physics, Beijing, China have published a paper in the Proceeding of the National Academy of Sciences (Vol. 112, pg. 2367) titled "Classification of Charge Density Waves based on their Nature." This work is a result of a collaboration funded by the Chinese Academy of Science.

Charge Density Waves (CDWs) are observed in many solids, especially in low-dimensional systems. The existence of CDWs was first predicted in the 1930s by Sir Rudolf Peierls, who prophesied that CDWs would exist in an ideal one-dimensional (1-D) chain of atoms, lowering the energy of the system and driving a reconstruction of the lattice. The 1940 paper by Frisch and Peierls described how one could construct an atomic bomb from a small amount of uranium-235. In 1959, Walter Kohn (1998 Nobel Prize) pointed out that the origin of a CDW in the Peierls picture would result in what is now known as a "Kohn Anomaly", a simultaneous softening of coherent lattice vibrations, i.e., phonon softening. This simple text-book picture of the origin of CDWs does not seem to be correct in most if not all materials, so in this report we propose a new classification of CDWs based upon their nature.