C-AXIS RESPONSE OF SINGLE-LAYERED AND DOUBLE-LAYERED CUPRATES

We report on an infrared study of the c-axis response of the single-layered superconductor La2-xSrxCuO4 (T-c=34 K) and analyze the results in comparison with our earlier data for the double-layered YBa2Cu4O8 [Basov et at, Phys. Rev. B 50, 3511 (2994)]. We find that in both materials nonmetallic temperature dependence of the de resistivity along the c axis results from the transfer of the spectral weight from the far-infrared region to much higher energies. The energy scale associated with this transfer in the normal state is about 200 cm(-1) in the double-layered system and exceeds 5000 cm(-1) in the single-layered material. No well-defined pseudogap is found in the latter case. The superconducting state in both systems is highly unusual since the spectral weight of the superfluid delta function peak is accumulated from the frequencies as high as 20 k T-c.