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What is the lower critical dimension (LCD) of the bond-diluted Ising model?

Physics Asked by valerio on June 1, 2021

It is known that the lower critical dimension (LCD) $d_l$ of the Ising model is $d_l=1$, that the LCD of the Edwards-Anderson model is $d_l=5/2$ (source) and that the LCD of the random field Ising model is $d_l=2$ (source).

My question is: what is the LCD of the bond-diluted Ising model?

The bond-diluted Ising model is defined by the hamiltonian

$$H = – sum_{langle ij rangle} J_{ij} sigma_i sigma_j$$

where the sum runs over nearest neighbors, $sigma_i=pm 1$ are the usual spin variables and $J_{ij}$ is $1$ with probability $p$ and $0$ with probability $1-p$.

Clarification: I know that there can be no phase transition in $d=1$ because the one-dimensional bond percolation threshold is $p_c(1)=1$ and a phase transition is possible only if $p>p_c(d)$ (see Yvan Velenkis’s answer and following comments), but I was wondering whether more general results including non-integer dimensions are available (see this paper and this paper for examples of discussions where the dimension is treated as a real variable).

One Answer

If the bonds of the two-dimensional square lattice are removed independently with probability $p$, then there is a phase transition for the Ising model on the resulting graph, at large enough $beta$, for any $p>p_{rm c}(2)$, where $p_{rm c}(2)=tfrac12$ is the critical percolation threshold for bond percolation on $mathbb{Z}^2$.

The first (rigorous) proof, as far as I know, can be found in H.-O. Georgii, Spontaneous magnetization of randomly dilute ferromagnets, J. Statist. Phys. 25 (1981), no. 3, 369-396.

Answered by Yvan Velenik on June 1, 2021

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