Oxygen Isotope Effects on Lattice Properties of La_{2-x}Ba_xCuO_4 (x = 1/8)

TL;DR

This study reveals a negative oxygen-isotope effect on the structural and electronic phase transitions in La_{2-x}Ba_xCuO_4 (x=1/8), highlighting the role of anharmonic electron-lattice interactions in cuprate stripe phases.

Contribution

It provides the first evidence of isotope effects on the LTT transition and charge ordering, emphasizing the importance of anharmonic lattice interactions in high-temperature superconductors.

Findings

Negative isotope effect on T_{LTT} transition temperature

Correlation between isotope effects on T_{LTT} and T_{so}

Shortening of c-axis with heavier isotope

Abstract

A novel negative oxygen-isotope (16O/18O) effect (OIE) on the low-temperature tetragonal phase transition temperature T_{LTT} was observed in La_{2-x}Ba_xCuO_4 (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.