Emergence of a Boundary-Sensitive Phase in Hyperbolic Ising Models

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Main Authors: Wang, Xingzhi, Nussinov, Zohar, Ortiz, Gerardo
Format: Preprint
Published: 2025
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author Wang, Xingzhi
Nussinov, Zohar
Ortiz, Gerardo
author_facet Wang, Xingzhi
Nussinov, Zohar
Ortiz, Gerardo
contents Physical systems defined on hyperbolic lattices may exhibit phases of matter that only emerge due to negative curvature. We focus on the case of the Ising model under open boundary conditions and show that an ``intermediate'' phase emerges in addition to standard (high-temperature) paramagnetic and (low-temperature) ferromagnetic phases. When performing the Kramers-Wannier duality the fact that it alters boundary conditions becomes crucial, since a finite fraction of lattice sites lie on the boundary. We propose to characterize this ``intermediate'' phase by its sensitivity to boundary conditions, wherein bulk ordering is not spontaneous but rather induced by boundary effects, setting it apart from the Landau paradigm of spontaneous symmetry breaking. By developing a $\mathbb{Z}_2$ symmetry restricted extension of the Corner Transfer Matrix Renormalization Group method, we provide numerical evidence for the existence of all three distinct phases and their corresponding two-stage phase transitions, thereby establishing the complete phase diagram. We also establish how the (spontaneous) intermediate-to-ferromagnetic and the (induced) paramagnetic-to-intermediate transition points are related by the Kramers-Wannier duality relation. We discuss a holographic correspondence between boundary and bulk behaviors and derive exact expressions for boundary correlation functions on Cayley trees.
format Preprint
id arxiv_https___arxiv_org_abs_2507_21044
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Emergence of a Boundary-Sensitive Phase in Hyperbolic Ising Models
Wang, Xingzhi
Nussinov, Zohar
Ortiz, Gerardo
Statistical Mechanics
Disordered Systems and Neural Networks
Soft Condensed Matter
Mathematical Physics
Physical systems defined on hyperbolic lattices may exhibit phases of matter that only emerge due to negative curvature. We focus on the case of the Ising model under open boundary conditions and show that an ``intermediate'' phase emerges in addition to standard (high-temperature) paramagnetic and (low-temperature) ferromagnetic phases. When performing the Kramers-Wannier duality the fact that it alters boundary conditions becomes crucial, since a finite fraction of lattice sites lie on the boundary. We propose to characterize this ``intermediate'' phase by its sensitivity to boundary conditions, wherein bulk ordering is not spontaneous but rather induced by boundary effects, setting it apart from the Landau paradigm of spontaneous symmetry breaking. By developing a $\mathbb{Z}_2$ symmetry restricted extension of the Corner Transfer Matrix Renormalization Group method, we provide numerical evidence for the existence of all three distinct phases and their corresponding two-stage phase transitions, thereby establishing the complete phase diagram. We also establish how the (spontaneous) intermediate-to-ferromagnetic and the (induced) paramagnetic-to-intermediate transition points are related by the Kramers-Wannier duality relation. We discuss a holographic correspondence between boundary and bulk behaviors and derive exact expressions for boundary correlation functions on Cayley trees.
title Emergence of a Boundary-Sensitive Phase in Hyperbolic Ising Models
topic Statistical Mechanics
Disordered Systems and Neural Networks
Soft Condensed Matter
Mathematical Physics
url https://arxiv.org/abs/2507.21044