Universality class of interacting k-mers in a two-dimensional lattice system

F. ROMÁ; A.J. RAMIREZ PASTOR; J.L. RICCARDO

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Institute of Physics

Año: 2005 vol. 72 p. 354441 - 354448

0163-1829

Monte Carlo simulations and finite-size scaling analysis have been carried out to study the critical behavior in a submonolayer two-dimensional gas of repulsive linear k-mers on a square lattice at half coverage. A 2k2 ordered phase, characterized by alternating files of k-mers separated by k adjacent empty sites, is separated from the disordered state by a order-disorder phase transition occurring at a finite critical temperature. Based on the strong axial anisotropy of the low-temperature phase for k2, an order parameter measuring the orientation of the particles has been introduced. Taking advantage of its definition, an accurate determination of the critical exponents has been obtained for three adsorbate sizes. Namely, =0.531, =0.021, =1.143, and =0.933 for k=2 dimers; =0.541, =0.031, =1.163, and=0.893 for k=3 trimers; and =0.532, =0.021, =1.143, and =0.894 for k=4 tetramers. Inthe studied cases, the results reveal that the system does not belong to the universality class of the twodimensional Ising model k=1, monomers. We pointed out that the breaking of the orientational symmetry characterizing the low-temperature phase for particles occupying more than one site is the main source of this change in the universality class. Consequently, we suggested that the behavior observed for dimers, trimers, and tetramers could be generalized to include larger particle sizes k2. Finally, hyperscaling relations have been validated, leading to independent controls and consistency checks of the values of all the critical exponents.