Evidence for a Peierls Distortion in La sub 2 Cu O sub 4 from Vibrational Spectroscopy

Two features have been observed in the infrared absorption spectrum of the new superconductors La sub 2-x Sr sub x Cu O sub 4. The higher frequency feature at 677 cm sup -1 in La sub 2 CuO sub 4 dominates the spectrum for x = 0. However, small Sr replacements (x ~> 0.03) cause the 677 cm sup -1 band to be reduced dramatically in intensity and to disappear entirely by x = 0.15.