Raman study of ordering phenomena in copper–oxygen systems

Abstract

We summarize results of light-scattering experiments in underdoped La 2− x Sr x CuO 4 (LSCO) and YBa 2 Cu 3 O 6+ x (Y-123) single crystals. Below a doping-dependent temperature close to the pseudogap cross-over line T *( p ) new peaks appear in the low-energy part of the spectra. For low doping, p ≃ 0.02 holes per CuO 2 , the features are observed in B 2g symmetry in both LSCO and Y-123. At p =0.10 the additional contribution exists only in LSCO and is found at B 1g symmetry. We interpret the low-energy peaks in terms of a charge ordering instability. The ‘stripes’ are fluctuating with preferential orientation along the diagonals and the principle axes at p ≃ 0.02 and p =0.10, respectively.