Logarithmic delocalization of low temperature 3D Ising and Potts interfaces above a hard floor

TL;DR

This paper demonstrates that in low temperature 3D Ising and Potts models, the interface height above a hard floor diverges logarithmically with system size, showing entropic repulsion overcomes boundary attraction.

Contribution

It establishes a logarithmic lower bound and a conjecturally sharp upper bound on interface height for both models, extending understanding beyond the Ising case.

Findings

Interface height diverges logarithmically with system size.

Entropic repulsion dominates boundary attraction in both models.

Provides bounds using coupled random-cluster and fuzzy Potts models.

Abstract

We study the entropic repulsion of the low temperature 3D Ising and Potts interface in an $n\times n \times n$ box with blue boundary conditions on its bottom face (the hard floor), and red boundary conditions on its other five faces. For Ising, Frohlich and Pfister proved in 1987 that the typical interface height above the origin diverges (non-quantitatively), via correlation inequalities special to the Ising model; no such result was known for Potts. We show for both the Ising and Potts models that the entropic repulsion fully overcomes the potentially attractive interaction with the floor, and obtain a logarithmically diverging lower bound on the typical interface height. This is complemented by a conjecturally sharp upper bound of $\lfloor \xi^{-1}\log n\rfloor$ where $\xi$ is the rate function for a point-to-plane non-red connection under the infinite volume red measure. The proof goes through a coupled random-cluster interface to overcome the potential attractive interaction with the boundary, and a coupled fuzzy Potts model to reduce the upper bound to a simpler setting where the repulsion is attained by conditioning a no-floor interface to lie in the upper half-space.