Interactive companion to S. H. Lee, H. Jeong & J. D. Noh, Phys. Rev. E 74, 031118 (2006)

The random-field Ising model on scale-free networks

Every node carries a spin si = ±1. Links pull neighbours into line (J = 1); a quenched field hi drawn from p(h) = p0(h/Δ)/Δ pulls each spin its own way. Below, the exact zero-temperature ground state of H = −Σsisj − Σhisi is recomputed with a min-cut / max-flow solver (Dinic’s algorithm) whenever you move a control.

Random-field shape p0(x)
spin upspin downbroken bondspin against its own field

Mean-field theory

Assuming uncorrelated degrees and mi = m(ki, hi), the zero-temperature order parameter solves m = f(m) = ∫dk [kP(k)/k̄] G(km/Δ), with G(x) = 2∫0xp0. The shape of f near m = 0 decides everything (paper Fig. 1): an infinite slope means order at every Δ, convexity gives a jump, concavity a continuous transition. Curves here use the continuum P(k) = ck−γ for k ≥ k0, with k0 set by k̄.

Self-consistency map

Mean-field order parameter

What the theory predicts here

β(γ) from mean field (line) and the paper’s finite-size-scaling estimates (dots, Fig. 7).

Finite-size simulation

This reproduces the paper’s numerical test on static-model networks (Figs. 2–6): for each size, many independent networks and field realizations are solved exactly across a grid of Δ. The same realization is reused along Δ, as in a sweep. Larger sizes and more samples sharpen the picture but take longer; everything runs in your browser.

Network sizes N
Not run yet

Order parameter ⟨m⟩ versus Δ

Paper Figs. 2 and 4.

Binder parameter U = 1 − ⟨m4⟩ / 3⟨m2⟩2

Paper Fig. 5. Curves for different N cross at a continuous transition.

Histogram H(m) near the threshold

Paper Fig. 3. Two peaks at the same Δ signal phase coexistence and a first-order jump.

Finite-size scaling collapse

Paper Fig. 6: ⟨m⟩Nβ/ν′ versus |Δc − Δ|ν′N, using points with Δ < Δc.