Polarizability of a Wigner crystal

Abstract: We present a calculation of the imaginary part of the polarizability of a Wigner crystal using the Fluctuation-Dissipation theorem. The oscillations of the localized electrons about their equilibrium positions are treated in the harmonic approximation and the electric dipole-moment -- dipole-moment correlator is computed by a normal mode expansion. The amplitudes and phases of the different normal modes are assumed to be statistically independent. In the first case, polarizability is computed in the high temperature limit, $k_B T>>\hbar \Omega_W$ (here, $\Omega_W$ is the Wigner frequency, analogous to the Debye frequency of the phonon case). In the second case, a general expression (valid both at high and low temperature limits) is obtained using a phenomenological damping model. The connection between our general expression and that of the Lorentz oscillator model is discussed. It turns out that the Wigner crystal would be transparent for applied frequencies greater than the Wigner frequency. A standard ellipsometry set-up can test the predictions of the theory.