[article] Perustieteiden korkeakoulu / SCI

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Browsing [article] Perustieteiden korkeakoulu / SCI by Subject "3D Ising magnets"

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  • Percolation in three-dimensional random field Ising magnets
    (2002) Seppälä, E. T.; Pulkkinen, A. M.; Alava, Mikko J.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The structure of the three-dimensional (3D) random field Ising magnet is studied by ground-state calculations. We investigate the percolation of the minority-spin orientation in the paramagnetic phase above the bulk phase transition, located at [Δ/J]c≃2.27, where Δ is the standard deviation of the Gaussian random fields (J=1). With an external field H there is a disorder-strength-dependent critical field ±Hc(Δ) for the down (or up) spin spanning. The percolation transition is in the standard percolation universality class. Hc∼(Δ−Δp)δ, where Δp=2.43±0.01 and δ=1.31±0.03, implying a critical line for Δc<Δ<~Δp. When, with zero external field, Δ is decreased from a large value there is a transition from the simultaneous up- and down-spin spanning, with probability Π↑↓=1.00 to Π↑↓=0. This is located at Δ=2.32±0.01, i.e., above Δc. The spanning cluster has the fractal dimension of standard percolation, Df=2.53 at H=Hc(Δ). We provide evidence that this is asymptotically true even at H=0 for Δc<Δ<~Δp beyond a crossover scale that diverges as Δc is approached from above. Percolation implies extra finite-size effects in the ground states of the 3D random field Ising model.