Haefliger, P. S.3; Gerber, S.9; Pramod, R.5; Schnells, V. I.5; dalla Piazza, B.5; Chati, R.3; Pomjakushin, V.9; Conder, K.9; Pomjakushina, E.9; Le Dreau, L.9; Christensen, Niels Bech1; Syljuasen, O. F.6; Normand, B.7; Rønnow, Henrik Moodysson8
1 Department of Physics, Technical University of Denmark2 Neutrons and X-rays for Materials Physics, Department of Physics, Technical University of Denmark3 Swiss Federal Institute of Technology4 Paul Scherrer Institut5 École Polytechnique Fédérale de Lausanne6 University of Oslo7 Renmin University of China8 Risø National Laboratory for Sustainable Energy, Technical University of Denmark9 Paul Scherrer Institut
We study the zero-point and thermal ionic motion in La2CuO4 by means of high-resolution neutron-diffraction experiments. Our results demonstrate anisotropic motion of O and, to a lesser extent, Cu ions, both consistent with the structure of coupled CuO6 octahedra, and quantify the relative effects of zero-point and thermal contributions to ionic motion. By substitution of O-18, we find that the oxygen isotope effect on the lattice dimensions is small and negative (-0.01%), while the isotope effect on the ionic displacement parameters is significant (-6 to 50%). We use our results as input for theoretical estimates of the distribution of magnetic interaction parameters, J, in an effective one-band model for the cuprate plane. We find that ionic motion causes only small (1%) effects on the average value <J >, which vary with temperature and O isotope, but results in dramatic (10-20%) fluctuations in J values that are subject to significant (8-12%) isotope effects. We demonstrate that this motional broadening of J can have substantial effects on certain electronic and magnetic properties in cuprates.
Physical Review B (condensed Matter and Materials Physics), 2014, Vol 89, Issue 8