Subspace-Protected Topological Phases and Bulk-Boundary Correspondence

• URL: http://arxiv.org/abs/2508.20908v2
• Date: Sun, 14 Sep 2025 14:26:12 GMT
• Title: Subspace-Protected Topological Phases and Bulk-Boundary Correspondence
• Authors: Kenji Shimomura, Ryo Takami, Daichi Nakamura, Masatoshi Sato,
• Abstract summary: A subspace property for Hamiltonians enables us to define new topological invariants.<n>We establish and demonstrate the bulk-boundary correspondence in subspace-protected topological phases.
• Score: 0.0
• License: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Abstract: While tremendous research has revealed that symmetry enriches topological phases of matter, more general principles that protect topological phases have yet to be explored. In this Letter, we elucidate the roles of subspaces in free-fermionic topological phases. A subspace property for Hamiltonians enables us to define new topological invariants. It results in peculiar topological boundary phenomena, i.e., the emergence of an unpaired zero mode or zero-winding skin modes, characterizing subspace-protected topological phases. We establish and demonstrate the bulk-boundary correspondence in subspace-protected topological phases. We further discuss the interplay of the subspace property and internal symmetries. Toward application, we also propose possible platforms possessing the subspace property.

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