Observation of ring states in a delicate topological insulator
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arXiv
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| Main Authors: | , , , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866911601719771136 |
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| author | Tornow, Caroline Rupprecht, Julia Engeler, Pascal Drechsler, Ute Huhtinen, Kukka-Emilia Devescovi, Chiara Huber, Sebastian D. |
| author_facet | Tornow, Caroline Rupprecht, Julia Engeler, Pascal Drechsler, Ute Huhtinen, Kukka-Emilia Devescovi, Chiara Huber, Sebastian D. |
| contents | Topological insulators are typically characterized by particularly stable properties, such as global invariants, and can be identified by probing their robust surface states. A recently discovered novel form of band topology, delicate topology, challenges this paradigm: its defining property, multicellularity, can be removed by introducing a coupling to local orbitals anywhere in the spectrum, even far above the relevant band gap. This makes it hard to diagnose delicate topology with conventional probes that access only low-energy degrees of freedom. Here, we introduce strong local impurities as a spectroscopic probe of a delicate topological insulator which we realize in a phononic metamaterial. By tuning the impurity strength and performing orbital-resolved readout, we observe recently proposed indicators of topology: ring states, in-gap bound states whose frequencies remain pinned in the strong-impurity limit while their real-space profiles form a pronounced ring around the impurity site. We find that these ring states persist even when the multicellularity in our system is removed by a weakly hybridizing additional orbital. Our results establish impurity-induced ring states as probes of complex multiband physics, including delicate topological phases. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_15983 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Observation of ring states in a delicate topological insulator Tornow, Caroline Rupprecht, Julia Engeler, Pascal Drechsler, Ute Huhtinen, Kukka-Emilia Devescovi, Chiara Huber, Sebastian D. Mesoscale and Nanoscale Physics Topological insulators are typically characterized by particularly stable properties, such as global invariants, and can be identified by probing their robust surface states. A recently discovered novel form of band topology, delicate topology, challenges this paradigm: its defining property, multicellularity, can be removed by introducing a coupling to local orbitals anywhere in the spectrum, even far above the relevant band gap. This makes it hard to diagnose delicate topology with conventional probes that access only low-energy degrees of freedom. Here, we introduce strong local impurities as a spectroscopic probe of a delicate topological insulator which we realize in a phononic metamaterial. By tuning the impurity strength and performing orbital-resolved readout, we observe recently proposed indicators of topology: ring states, in-gap bound states whose frequencies remain pinned in the strong-impurity limit while their real-space profiles form a pronounced ring around the impurity site. We find that these ring states persist even when the multicellularity in our system is removed by a weakly hybridizing additional orbital. Our results establish impurity-induced ring states as probes of complex multiband physics, including delicate topological phases. |
| title | Observation of ring states in a delicate topological insulator |
| topic | Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2604.15983 |