Quantum and thermal ionic motion, oxygen isotope effect, and superexchange distribution in La2CuO4

P. S. Haefliger, S. Gerber, R. Pramod, V. I. Schnells, B. dalla Piazza, R. Chati, V. Pomjakushin, K. Conder, E. Pomjakushina, L. Le Dreau, Niels Bech Christensen, O. F. Syljuasen, B. Normand, Henrik Moodysson Rønnow

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Abstract

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.
Original languageEnglish
Article number085113
JournalPhysical Review B Condensed Matter
Volume89
Issue number8
Number of pages13
ISSN0163-1829
DOIs
Publication statusPublished - 2014

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