Exotic massive fermionic systems with huge vacuum degeneracy at boundaries

TL;DR

This paper studies a non-relativistic fermionic system with boundary-induced vacuum degeneracy, revealing how boundary effects lead to extensive residual entropy proportional to boundary area, especially when the mass term is introduced.

Contribution

It uncovers the boundary-induced vacuum degeneracy in a massive fermionic system and analyzes how boundary effects influence the system's entropy and symmetry breaking.

Findings

Boundary introduces huge vacuum degeneracy proportional to boundary area.

Mass term breaks fermionic subsystem symmetry, leading to a gapped phase.

Residual entropy scales with boundary area, indicating boundary-dominated degeneracy.

Abstract

We investigate a massive non-relativistic fermionic system exhibiting exotic features. When the mass parameter is set to zero, the system acquires the fermionic subsystem symmetry. Introducing the mass term explicitly breaks this symmetry, resulting in a trivially gapped system in the absence of boundaries. We demonstrate that with the introduction of boundaries, the system remains gapped, but it has a huge vacuum degeneracy. The residual entropy is proportional to the area of the boundary.