Geometrical clusters in two-dimensional random-field Ising models.

We consider geometrical or Ising clusters (i.e., domains of parallel spins) in the square lattice random-field Ising model by varying the strength of the Gaussian random field Delta . In agreement with the conclusion of a previous investigation [Phys. Rev. E 63, 066109 (2001)], the geometrical correlation length, i.e., the average size of the clusters xi is finite for Delta>Delta_{c} approximately 1.65 and divergent for DeltaDelta_{c} . The scaling function of the distribution of the mass of the clusters as well as the geometrical correlation function are found to involve the scaling exponents of critical percolation. On the other hand, the divergence of the correlation length, xi(Delta) approximately (Delta-Delta_{c});{-nu} , with nu approximately 2 , is related to that of tricritical percolation. It is verified numerically that critical geometrical correlations transform conformally.