X-ray scattering study of charge density waves in La_2−xBa_xCuO₄

We report a comprehensive x-ray scattering study of charge density wave (stripe) ordering in La_2−xBa_xCuO₄ (x≈1∕8), for which the bulk superconducting T_c is greatly suppressed. Strong superlattice reflections corresponding to static ordering of charge stripes were observed in this sample. The structural modulation at the lowest temperature was deduced based on the intensity of over 70 unique superlattice positions surveyed. We found that the charge order in this sample is described with one-dimensional charge density waves, which have incommensurate wave vectors (0.23, 0, 0.5) and (0, 0.23, 0.5), respectively, on neighboring CuO₂ planes. The structural modulation due to the charge density wave order is simply sinusoidal, and no higher harmonics were observed. Just below the structural transition temperature, short-range charge density wave correlation appears, which develops into a large scale charge ordering around 40 K, close to the spin density wave ordering temperature. However, this charge ordering fails to grow into a true long range order, and its correlation length saturates at ∼230 Å, and slightly decreases below about 15 K, which may be due to the onset of two-dimensional superconductivity.