Experimental verification of critical exponents in the two-dimensional four-state Potts universality class: Oxygen on Ru(0001)

Abstract

Order-disorder critical behavior of the adsorption system O/Ru(0001) at (1/4 monolayer, ordered in a p(2\ifmmode\times\else\texttimes\fi{}2) structure, is studied by use of LEED. By measuring the profiles---and the peak and integrated intensities---of the (1/2-order oxygen LEED spots as function of temperature for 0.004\ensuremath{\Vert}(T-${\mathrm{T}}_{\mathrm{c}}$)/${\mathrm{T}}_{\mathrm{c}}$\ensuremath{\Vert}0.2, we determine the critical exponents \ensuremath{\alpha}, \ensuremath{\beta}, \ensuremath{\gamma}, and \ensuremath{\nu} independently. They agree to within 3% to 10% of the theoretical values for the two-dimensional four-state Potts model universality class.