Oxygen isotope effects on lattice properties of La2-xBaxCuO4 (x=1/8)

A negative oxygen-isotope (O-16/O-18) effect (OIE) on the low-temperature tetragonal (LTT) phase-transition temperature T-LTT was observed in La2-xBaxCuO4 (x = 1/8) using high-resolution neutron powder diffraction. The corresponding OIE exponent alpha T-LTT = -0.36(5) has the same sign as alpha T-so = -0.57(6) found for the spin-stripe order temperature T-so. The fact that the LTT transition is accompanied by charge ordering (CO) implies the presence of an OIE also for the CO temperature T-co. 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.