Structural response to local charge order in underdoped but superconducting La2-x(Sr,Ba)xCuO4

Results are presented of a local structural study of the nearest neighbor Cu-O distance distribution in underdoped but superconducting La1.875Sr0.125CuO4, La1.85Ba0.15CuO4 and La1.85Sr0.15CuO4. Atomic pair distribution function analysis of neutron powder diffraction data has been carried out to obtain local structural information over a wide temperature range. We observe an anomalous increase in the Cu-O bond length distribution at low temperature that may be associated with the presence of an inhomogeneous charge distribution. The increase at low temperature has an onset temperature which correlates with observations of charge and spin freezing seen by other probes.