Observation of an isolated flat band in the van der Waals crystal NbOCl$_2$
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arXiv
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| Autori principali: | , , , , , , , , , , , , , |
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| Natura: | Preprint |
| Pubblicazione: |
2026
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| _version_ | 1866909998947237888 |
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| author | Bao, Changhua Eggers, Vincent Meierhofer, Manuel Helml, Jakob Münster, Lasse Ito, Suguru Machtl, Leon Zajusch, Sarah Inzani, Giacomo Wittmann, Ludwig Liebich, Marlene Wallauer, Robert Höfer, Ulrich Huber, Rupert |
| author_facet | Bao, Changhua Eggers, Vincent Meierhofer, Manuel Helml, Jakob Münster, Lasse Ito, Suguru Machtl, Leon Zajusch, Sarah Inzani, Giacomo Wittmann, Ludwig Liebich, Marlene Wallauer, Robert Höfer, Ulrich Huber, Rupert |
| contents | Dispersionless electronic bands lead to an extremely high density of states and suppressed kinetic energy, thereby increasing electronic correlations and instabilities that can shape emergent ordered states, such as excitonic, ferromagnetic, and superconducting phases. A flat band that extends over the entire momentum space and is well isolated from other dispersive bands is, therefore, particularly interesting. Here, the band structure of the van der Waals crystal NbOCl$_2$ is revealed by utilizing photoelectron momentum microscopy. We directly map out an electronic band that is flat throughout the entire Brillouin zone and features a width of only $\sim$100 meV. This band is well isolated from both the conduction and remote valence bands. Moreover, the quasiparticle band gap shows a high tunability upon the deposition of caesium atoms on the surface. By combining the single-particle band structure with the optical transmission spectrum, the optical gap is identified. The fully isolated flat band in a van der Waals crystal provides a qualitatively new testbed for exploring flat-band physics. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_16688 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Observation of an isolated flat band in the van der Waals crystal NbOCl$_2$ Bao, Changhua Eggers, Vincent Meierhofer, Manuel Helml, Jakob Münster, Lasse Ito, Suguru Machtl, Leon Zajusch, Sarah Inzani, Giacomo Wittmann, Ludwig Liebich, Marlene Wallauer, Robert Höfer, Ulrich Huber, Rupert Mesoscale and Nanoscale Physics Materials Science Strongly Correlated Electrons Dispersionless electronic bands lead to an extremely high density of states and suppressed kinetic energy, thereby increasing electronic correlations and instabilities that can shape emergent ordered states, such as excitonic, ferromagnetic, and superconducting phases. A flat band that extends over the entire momentum space and is well isolated from other dispersive bands is, therefore, particularly interesting. Here, the band structure of the van der Waals crystal NbOCl$_2$ is revealed by utilizing photoelectron momentum microscopy. We directly map out an electronic band that is flat throughout the entire Brillouin zone and features a width of only $\sim$100 meV. This band is well isolated from both the conduction and remote valence bands. Moreover, the quasiparticle band gap shows a high tunability upon the deposition of caesium atoms on the surface. By combining the single-particle band structure with the optical transmission spectrum, the optical gap is identified. The fully isolated flat band in a van der Waals crystal provides a qualitatively new testbed for exploring flat-band physics. |
| title | Observation of an isolated flat band in the van der Waals crystal NbOCl$_2$ |
| topic | Mesoscale and Nanoscale Physics Materials Science Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2601.16688 |