Raman study of ordering phenomena in copper–oxygen systems

We summarize results of light-scattering experiments in underdoped La2−xSrxCuO4 (LSCO) and YBa2Cu3O6+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 CuO2, the features are observed in B2g symmetry in both LSCO and Y-123. At p=0.10 the additional contribution exists only in LSCO and is found at B1g 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.