Anomalies in the ab-plane resistivity of strongly underdoped La₂₋ₓSrₓCuO₄ single crystals: possible charge stripe ordering?

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We present and discuss the results of measurements of the ab-plane resistivity of La₂₋ₓSrₓCuO₄ single crystals with small Sr contents (x=0.052-0.075). The resistivity was obtained in the temperature range between 4.2 K and 300 K by using an AC Van der Pauw technique. When the temperature is lowered, the rhoab(T) curves show a transition from a linear behaviour to a semiconducting-like one. The deviation from the linearity occurs at a doping-dependent temperature Tch. This effect can be interpreted as due to a progressive pinning of preexistent charge stripes. In the same framework, the appearance of anomalous sharp peaks in the rhoab(T) curves of superconducting samples just above Tc may be explained by a transition from a nematic to a more ordered smectic electronic stripe phase.