Fingerprints of charge ordering in anelastic spectra of underdoped La_2-xSr_xCuO₄

We carefully investigate the anelastic spectra of La_2-xSr_xCuO₄ (x = 0.02-0.08) from 90 to 300 K at kHz range. Two internal friction peaks are observed near 130 and 160 K, respectively, whose amplitudes demonstrate crossovers around the insulating-superconducting phase boundary (x_C ∼ 0.055). The 160 K peak is of phase-like transition character and originates from the localization of diagonal charge stripes by LTO lattice and the resultant lattice adjustment. The origin of the 130 K relaxation is discussed in the framework of structural inhomogeneity as a combined result of charge inhomogeneity and electron-phonon coupling.