THE AB-PLANE OPTICAL CONDUCTIVITY OF HIGH-T-C SUPERCONDUCTORS

There is anisotropy in the ab-plane optical properties of the high-temperature superconductors, both in the normal state and in the superconducting state. In both states, two components appear in the optical conductivity: a free carrier part and a ''midin-frared'' component. Below T-c, the free carriers form the superconducting condensate. In YBa2CU3O7-delta, the anisotropy of the penetration depth shows that the chains contribute strongly to this superfluid. In Bi2Sr2CaCu2O8, where chains are absent, there is still ab plane anisotropy. Below Te a finite absorption parallel b remains at frequencies as small as 20 meV. This anisotropy could be due to anisotropy either of the superconducting gap or the midinfrared component.