Wave-vector orientation of a charge-density wave in potassium

Abstract

A criterion for the preferred direction of the wave vector $\overrightarrow{\mathrm{Q}}$ of a charge-density wave (CDW) is obtained by means of a simple theory. Screening of the electric field caused by the CDW is provided by a sinusoidal distortion of the positive-ion lattice. The optimum $\overrightarrow{\mathrm{Q}}$ direction is that which minimizes the elastic energy of distortion. For potassium the $\overrightarrow{\mathrm{Q}}$ direction is found to be tilted about 4° away from a [110] direction. The exact value of the tilt depends on the magnitude of $\overrightarrow{\mathrm{Q}}$.