Fluctuating stripes at the onset of the pseudogap in the high-T_c superconductor Bi₂Sr₂CaCu₂O_8+x

Doped Mott insulators have a strong propensity to form patterns of holes and spins often referred to as stripes^{1, 2, 3, 4, 5}. In copper oxides, doping also gives rise to the pseudogap state⁶, which can be transformed into a high-temperature superconducting state with sufficient doping or by reducing the temperature. A long-standing issue has been the interplay between the pseudogap, which is generic to all hole-doped copper oxide superconductors, and stripes, whose static form occurs in only one family of copper oxides over a narrow range of the phase diagram^{2, 7}. Here we report observations of the spatial reorganization of electronic states with the onset of the pseudogap state in the high-temperature superconductor Bi₂Sr₂CaCu₂O_8+x, using spectroscopic mapping with a scanning tunnelling microscope. We find that the onset of the pseudogap phase coincides with the appearance of electronic patterns that have the predicted characteristics of fluctuating stripes⁸. As expected, the stripe patterns are strongest when the hole concentration in the CuO₂ planes is close to 1/8 (per copper atom)^{2, 3, 4, 5, 8}. Although they demonstrate that the fluctuating stripes emerge with the onset of the pseudogap state and occur over a large part of the phase diagram, our experiments indicate that the stripes are a consequence of pseudogap behaviour rather than its cause.