Finite-size scaling of the density of zeros of the partition function in first- and second-order phase transitions

The finite-size scaling form for the density of zeros of the partition function in first-and second-order phase transitions is derived. Using the finite-size scaling of the density of zeros, the order of a phase transition can be easily determined and the order parameter calculated from finite-size data. We illustrate the scaling theory using exact values for the zeros of the partition function of the two-dimensional Ising model in the complex magnetic-field plane.