Optical phonons of superconducting infinite-layer compounds Sr(0.9)Ln(0.1)CuO(2) (Ln = La and Sm)

We have identified the optical phonon modes of high-quality superconducting infinite-layer compounds Sr(0.9)Ln(0.1)CuO(2) (Ln = La and Sm. T-c = 43 K for both) from their infrared reflectivity spectra obtained with a Fourier- transform infrared spectrometer. The La-doped compound exhibited only four (2A(2u) + 2E(u)) out of the five (2A(2u) + 3E(u)) infrared-active phonon mo des predicted by a group theoretical analysis, with one E-u mode screened b y free carriers. The Sm-doped compound exhibited all five modes. We propose the displacement pattern for each mode based on reported lattice dynamics calculations and through comparison with the phonon modes of other single-l ayer high-T-c cuprates. (C) 2001 Elsevier Science B.V. All rights reserved.