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| Main Authors: | , , , , |
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| Format: | Preprint |
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2024
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2412.13456 |
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| _version_ | 1866909881171181568 |
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| author | Khan, Mahtab A. Din, Naseem Ud Skachkov, Dmitry Englund, Dirk R. Leuenberger, Michael N. |
| author_facet | Khan, Mahtab A. Din, Naseem Ud Skachkov, Dmitry Englund, Dirk R. Leuenberger, Michael N. |
| contents | Flat electronic bands strongly enhance Coulomb interactions and can stabilize unconventional insulating states. Motivated by the recent discovery of flat bands in breathing Kagome lattices, we use first-principles GW--Bethe--Salpeter theory to investigate the excitonic spectrum of single-layer Nb$_3$Cl$_8$. We find a dark spin-triplet Frenkel exciton whose spectral peak lies at negative energy ($-0.14$~eV) relative to the quasiparticle gap, directly signaling a preformed bound state and an excitonic Mott insulating phase potentially stable at room temperature. Bright excitons appear at $0.94$~eV and $1.21$~eV, with ultra-large binding energies of $2.05$~eV and $1.77$~eV. By mapping the low-energy dynamics onto a spin-1 Hubbard model on a triangular lattice, we show that frustrated antiferromagnetic and ferroelectric tendencies naturally emerge. These results identify Nb$_3$Cl$_8$ as a candidate multiferroic dark excitonic insulator, opening a pathway to correlated quantum phases in two dimensions. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2412_13456 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Multiferroic Dark Excitonic Mott Insulator in the Breathing-Kagome Lattice Material Nb$_3$Cl$_8$ Khan, Mahtab A. Din, Naseem Ud Skachkov, Dmitry Englund, Dirk R. Leuenberger, Michael N. Materials Science Flat electronic bands strongly enhance Coulomb interactions and can stabilize unconventional insulating states. Motivated by the recent discovery of flat bands in breathing Kagome lattices, we use first-principles GW--Bethe--Salpeter theory to investigate the excitonic spectrum of single-layer Nb$_3$Cl$_8$. We find a dark spin-triplet Frenkel exciton whose spectral peak lies at negative energy ($-0.14$~eV) relative to the quasiparticle gap, directly signaling a preformed bound state and an excitonic Mott insulating phase potentially stable at room temperature. Bright excitons appear at $0.94$~eV and $1.21$~eV, with ultra-large binding energies of $2.05$~eV and $1.77$~eV. By mapping the low-energy dynamics onto a spin-1 Hubbard model on a triangular lattice, we show that frustrated antiferromagnetic and ferroelectric tendencies naturally emerge. These results identify Nb$_3$Cl$_8$ as a candidate multiferroic dark excitonic insulator, opening a pathway to correlated quantum phases in two dimensions. |
| title | Multiferroic Dark Excitonic Mott Insulator in the Breathing-Kagome Lattice Material Nb$_3$Cl$_8$ |
| topic | Materials Science |
| url | https://arxiv.org/abs/2412.13456 |