Oxygen isotope effect on structural parameters and on the thermal motion in La$_2$CuO$_4$

TL;DR

This study investigates how oxygen isotope substitution affects structural parameters and atomic thermal motions in La$_2$CuO$_4$, revealing subtle isotope-induced changes in lattice constants and atomic vibrations at low temperatures.

Contribution

The paper provides detailed neutron diffraction analysis of isotope effects on structural and thermal parameters in La$_2$CuO$_4$, highlighting isotope-dependent variations in lattice and atomic motion.

Findings

Negative isotope effect on lattice parameters (-0.01%)

Positive isotope effect on thermal parameters for La and Cu

Significant isotope effect on La thermal motion at 15 K (up to 100%)

Abstract

We studied the oxygen isotope effect (OIE) on the zero point motion and the thermal motion as well as on structural parameters in La$_2$CuO$_4$ by means of high-resolution neutron diffraction experiments. We found a negative OIE on the lattice parameters (-0.01%). The OIE on the isotropic thermal parameters turned out to be positive for lanthanum, copper and negative for the oxygen atoms, respectively. The Rietvield refinement of the anisotropic thermal parameters of the different directions yielded the same sign of the OIE for each ion. Our analysis shows that the OIE on isotropic thermal parameters is most pronounced for La at 15 K (up to 100%) which we found to be originating mainly from the thermal motion in x-direction as determined from the refinement of the anisotropic thermal parameters.