Relaxation and tunnelling of structural units within the LTO phase of La2CuO4

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Cannelli, G.
Cantelli, R.
Cordero, F.
Grandini, Carlos Roberto [UNESP]

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Editrice Compositori Bologna


The anelastic relaxation (elastic energy loss and Young modulus) of nearly stoichiometric La2CuO4+delta with LTO structure was measured. Extraordinarily intense effects are present below room temperature in the elastic dynamic susceptibility, indicating relaxational dynamics of a relevant fraction of the lattice. The involved degrees of freedom are identified as rotations of the CuO6 octahedra. Two distinct processes are found at frequencies around 1 kKz: one is observed around 150 K and is characterized by a mean activation energy of 2800 K; the second one occurs below 30 K and is governed by atomic tunnelling. Two explanations are proposed for the faster process: i) formation of fluctuating LTT domains on a scale of few atomic cells; ii) the LTO phase is a dynamical Jahn-Teller phase with all the octahedra tunneling between two LTT-like tilts. In both cases there would be important implications regarding the mechanisms giving rise to charge nanophase separation and strong electron-phonon coupling.



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Nuovo Cimento Della Societa Italiana Di Fisica D-condensed Matter Atomic Molecular and Chemical Physics Fluids Plasmas Biophysics. Bologna: Editrice Compositori Bologna, v. 20, n. 7-8, p. 1127-1134, 1998.