Velocity renormalization in a quasi–two-dimensional electron gas

It is shown that for a quasi–two-dimensional electron gas embedded in a material with a large dielectric constant ε, the plasma frequency ω_p(q) for small momenta q may be less than the quasi-particle excitation energy υ(k_F) ∙ q. Under this condition, the screening of the Coulomb interaction is determined by the single-particle density of states. This gives rise to a significant increase of the velocity υ near the Fermi surface and, in turn, to an anomalous renormalization of the transport properties. The results are applied to explain the normal properties of the high-T_csuperconductors.