Negative differential conductivity of electrons in pure rare gases

A mechanism for negative differential conductivity (NDC) in pure rare gases is presented. The drift velocity of electrons in these gases has been calculated using the two-term expansion of the anisotropic electron energy distribution function in Legendre polynomials. In ionized rare gases (viz. Ar, Kr, and Xe), Coulombic collisions cause electron drift velocity to become a decreasing function of the electric field for specific energy levels and over a certain range of electric field strength. A detailed investigation of the effect of Coulomb interactions and electron collisions with excited atoms on NDC has been performed.