Tilt waves dynamics of the oxygen octahedra in La2CuO4 from anelastic and 139La NQR relaxation

TL;DR

This study investigates the anharmonic tilt wave dynamics of CuO6 octahedra in La2CuO4 using anelastic and La-139 NQR relaxation, revealing soliton-like tilt waves linked to lattice stripe phenomena in high-Tc superconductors.

Contribution

It introduces a model of tilt wave dynamics in La2CuO4, connecting local octahedral motions to macroscopic lattice stripe behavior in high-temperature superconductors.

Findings

Identified a relaxation peak related to octahedral tilt motion.

Derived an activation energy of 2800 K for the tilt dynamics.

Linked tilt wave behavior to lattice stripe phenomena in superconductors.

Abstract

The anharmonic vibrational dynamics in nearly stoichiometric La2CuO4+delta is studied by means of anelastic and ^{139}La NQR relaxation. In the absorption component of the elastic susceptibility as well as in the nuclear relaxation rate a peak is detected as a function of temperature, and a relaxation time tau = 1.7 10^{-12} exp [(2800 K)/T] s is derived. The relaxation processes are attributed to tilt motion of the CuO6 octahedra in doublewell potentials, whose cooperative character increases the effective energy barrier to the observed value. The analysis of the relaxation mechanisms has been carried out by reducing the dynamics of the interacting octahedra to a one-dimensional equation of motion. The soliton-like solutions correspond to parallel walls separating domains of different tilt patterns and give rise to pseudo-diffusive modes which appear as a central component in the spectral density of the motion of the octahedra. The tilt waves may be considered to correspond to the dynamical lattice stripes observed in La-based and Bi-based high-Tc superconductors.