Anelastic relaxation process of polaronic origin in La2-xSrxCuO4: interaction between charge stripes and pinning centers

The evolution of an anelastic relaxation process occurring around 80 K in La2-xSrxCuO4 at a measuring frequency of ~1 kHz has been followed from x=0.0075 to the overdoped region x=0.2, where it disappears.The dependence of the peak intensity on doping is consistent with a polaronic mechanism, identified with the disordered charge stripes overcoming pinning centers. A marked decrease of the peak amplitude and of the effective energy barrier for relaxation occurs at x~0.045, the same doping range where a change of the stripe order from parallel to diagonal with respect to the Cu-O bonds has been observed by neutron diffraction. Both the energy barrier and peak amplitude also exhibit a rise near x=1/8.