Phonon anomaly at 100-150K in La2-xSrxCuO4

Abstract Far infra-red spectroscopy of La2-xSrxCuO4, 0.03≤x≤0.24, compounds show weak phonon softening at 100–150K in underdoped samples and, at a slightly lower temperature, in 0.15 and 0.17 Sr LSCO. The maximum phonon renormalisation is 0.1% which is much weaker than 1% as observed in YBCO compounds. Assuming that the phonon renormalisations is LSCO and in YBCO have the same origin we conclude that (a) the correlation of phonon anomalies and local lattice distortions with the opening of a spin gap should be reconsidered, and (b) if magnetic excitations do drive the above phenomena then a spin gap should also exist in LSCO.