Critical fluctuations and quenched disordered two-dimensional charge stripes in La5/3Sr1/3NiO4

Using high-resolution x-ray scattering, we have demonstrated the existence of quenched disordered charge stripes in a single crystal of La5/3Sr1/3NiO4 at low temperatures. Above the second-order transition critical scattering was observed due to fluctuations into the charge stripe phase. 

The charge stripes are shown to be two dimensional in nature both by measurements of their correlation lengths (xi (a) = 185 Angstrom, xi (b) = 400 Angstrom, xi (c) = 25 Angstrom.) and by the critical exponents of the charge stripe transition. The charge stripe ordering did not develop long-range order even at low temperatures, indicating that the charge snipes are disordered and that the length scale of the disorder is quenched. Detailed measurements of the correlation lengths at higher temperatures, just below the charge stripe melting temperature, display an anisotropic broadening indicative of an order-disorder transition. 

We ascribe these results to a smectic-nematic phase transition at approximately 225 K. Such electronic quantum liquid-crystal phase transitions have been theoretically predicted before, but these results provide the first experimental evidence for them in charge stripe nickelates.