Abstract
Using high-resolution x-ray scattering, we have demonstrated the existance of quenched disordered charge stripes in a single crystal of La
5/3
Sr
1/3
NiO
4
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 (ξ
a
≈185 Å, ξ
b
≈400 Å, ξ
c
≈25 Å.) and by the critical exponents of the charge stripe transition. The charge stripes 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.