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

We report on an infrared study of the c-axis response of the single-la yered superconductor La2-xSrxCuO4 (T-c=34 K) and analyze the results i n comparison with our earlier data for the double-layered YBa2Cu4O8 [B asov et at, Phys. Rev. B 50, 3511 (2994)]. We find that in both materi als 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 w ith this transfer in the normal state is about 200 cm(-1) in the doubl e-layered system and exceeds 5000 cm(-1) in the single-layered materia l. No well-defined pseudogap is found in the latter case. The supercon ducting state in both systems is highly unusual since the spectral wei ght of the superfluid delta function peak is accumulated from the freq uencies as high as 20 k T-c.