Permanent polarization of small metallic particles

Electric charge density in a metallic particle fluctuates due to inhomogeneities of various kinds. While in the bulk of the particle the charge fluctuations are suppressed by Thomas-Fermi screening, the underscreened charges near the surface give rise to a permanent electric dipole moment. We show that the dipole moment increases linearly with the particle size, and fluctuates strongly from particle to particle.