Axion electrodynamics and giant magnetic birefringence in Weyl excitonic insulators
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| Format: | Preprint |
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2025
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| _version_ | 1866911304894119936 |
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| author | Grigoreva, Anna Andreev, Anton Glazman, Leonid |
| author_facet | Grigoreva, Anna Andreev, Anton Glazman, Leonid |
| contents | We study the electromagnetic (EM) response of the excitonic insulator phase of a time-reversal (TR) invariant Weyl semimetal (WSM). At low temperatures, the system develops two exciton condensates. The condensates are related to each other by TR symmetry and weakly coupled by a Josephson tunneling term. The latter leads to the formation of the Leggett mode [Number-phase fluctuations in two-band superconductors, Prog. Theor. Phys. 36, 901 (1966).] with a small gap. Our main finding is that the Leggett mode couples to the EM fields as a massive dynamical axion. This is a consequence of the chiral anomaly and the chiral magnetic effect in the parent WSM. Because of the small axion mass, its coupling to EM fields results in a giant anisotropic polarizability and birefringence in the presence of a static magnetic field. The photon-axion hybridization produces a polariton resonance near the axion gap. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2502_20456 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Axion electrodynamics and giant magnetic birefringence in Weyl excitonic insulators Grigoreva, Anna Andreev, Anton Glazman, Leonid Mesoscale and Nanoscale Physics We study the electromagnetic (EM) response of the excitonic insulator phase of a time-reversal (TR) invariant Weyl semimetal (WSM). At low temperatures, the system develops two exciton condensates. The condensates are related to each other by TR symmetry and weakly coupled by a Josephson tunneling term. The latter leads to the formation of the Leggett mode [Number-phase fluctuations in two-band superconductors, Prog. Theor. Phys. 36, 901 (1966).] with a small gap. Our main finding is that the Leggett mode couples to the EM fields as a massive dynamical axion. This is a consequence of the chiral anomaly and the chiral magnetic effect in the parent WSM. Because of the small axion mass, its coupling to EM fields results in a giant anisotropic polarizability and birefringence in the presence of a static magnetic field. The photon-axion hybridization produces a polariton resonance near the axion gap. |
| title | Axion electrodynamics and giant magnetic birefringence in Weyl excitonic insulators |
| topic | Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2502.20456 |