Electrical Resistivity Anisotropy from Self-Organized One Dimensionality in High-Temperature Superconductors

We investigate the manifestation of stripes in the in-plane resistivity anisotropy in untwinned single crystals of ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ ( $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.02--0.04$) and ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ ( $y\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}6.35--7.0$). It is found that both systems show strongly temperature-dependent in-plane anisotropy in the lightly hole-doped region and that the anisotropy in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ grows with decreasing $y$ below $\ensuremath{\sim}6.60$ despite the decreasing orthorhombicity, which gives most direct evidence that electrons self-organize into a macroscopically anisotropic state. The transport is found to be easier along the direction of the spin stripes already reported, demonstrating that the stripes are intrinsically conducting in cuprates.