= Landau mode
{c}
{title2=$\epsilon_{\mathbf k}(\omega_j)=0$}
A pole of the causally continued collective kinetic response, usually a zero of its scalar response denominator or response-matrix determinant. With time dependence $e^{-i\omega_jt}$, negative imaginary part gives damping, positive imaginary part growth, and zero imaginary part an undamped oscillation. Damped poles need not be regular discrete eigenmodes of the original collisionless operator: their contribution is obtained by continuing the initial-value response. The least damped excited pole can set the waiting time for a stationary forced response.
Back to article page
