Critical Exponents of a Four-State Potts Chemisorbed Overlayer:p(2×2)Oxygen on Ni(111)

Abstract

We report the first determination of critical exponents for a chemisorbed overlayer, using low-energy electron diffraction. We examine the order-disorder transition of $p(2\mathrm{}\times 2)$ oxygen on the (111) surface of nickel. This study is the first of critical behavior of a two-dimensional system in the four-state Potts universality class. From measured diffraction-beam profiles, we extract the exponents $\beta$, $\gamma$, and $\nu$. Discussion of disparity between our results and predicted exponents considers several possibilities, including logarithmic corrections.