Oxygen Isotope Effects on Lattice Properties of La2-xBaxCuO4 (x = 1/8)
Abstract
A novel negative oxygen-isotope (16O/18O) effect (OIE) on the low-temperature tetragonal phase transition temperature TLTT was observed in La2-xBaxCuO4 (x = 1/8) using high-resolution neutron powder diffraction. The corresponding OIE exponent alpha(TLTT) = - 0.36(5) has the same sign as alpha(Tso) = -0.57(6) found for the spin-stripe order temperature Tso. The fact that the LTT transition is accompanied by charge ordering (CO) implies the presence of an OIE also for the CO temperature Tco. Furthermore, a temperature dependent shortening of the c-axis with the heavier isotope is observed. These results combined with model calculations demonstrate that anharmonic electron-lattice interactions are essential for all transitions observed in the stripe phase of cuprates.