Interplay between Quantum Metric and Hybridized Collective Modes in Flat-Band Superfluids
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| Format: | Preprint |
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2026
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| _version_ | 1866913177579552768 |
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| author | Liu, Yi Wang, Mingyan Hu, Penghui Lu, Yao |
| author_facet | Liu, Yi Wang, Mingyan Hu, Penghui Lu, Yao |
| contents | We investigate collective excitations in flat-band superfluids by incorporating the coupled dynamics of pairing (phase and amplitude) and density fluctuations. We demonstrate that for any time-reversal symmetric superfluid system with an isolated flat band, only a single low-energy collective mode emerges in the long-wavelength limit. In contrast to the linearly dispersive Goldstone mode in conventional superfluids, this hybridized mode is gapless at zero momentum but exhibits a quadratic dispersion ($ω\propto q^2$) at small momenta. Analytically, we reveal that the dispersion coefficient of this collective mode is governed by the normal-state quantum metric of the flat band. These analytical predictions are in excellent agreement with numerical calculations. Our results are universally applicable to any generic $s$-wave flat-band superfluid, provided the flat band is energetically well separated from other dispersive bands. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2606_01235 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Interplay between Quantum Metric and Hybridized Collective Modes in Flat-Band Superfluids Liu, Yi Wang, Mingyan Hu, Penghui Lu, Yao Superconductivity Quantum Gases We investigate collective excitations in flat-band superfluids by incorporating the coupled dynamics of pairing (phase and amplitude) and density fluctuations. We demonstrate that for any time-reversal symmetric superfluid system with an isolated flat band, only a single low-energy collective mode emerges in the long-wavelength limit. In contrast to the linearly dispersive Goldstone mode in conventional superfluids, this hybridized mode is gapless at zero momentum but exhibits a quadratic dispersion ($ω\propto q^2$) at small momenta. Analytically, we reveal that the dispersion coefficient of this collective mode is governed by the normal-state quantum metric of the flat band. These analytical predictions are in excellent agreement with numerical calculations. Our results are universally applicable to any generic $s$-wave flat-band superfluid, provided the flat band is energetically well separated from other dispersive bands. |
| title | Interplay between Quantum Metric and Hybridized Collective Modes in Flat-Band Superfluids |
| topic | Superconductivity Quantum Gases |
| url | https://arxiv.org/abs/2606.01235 |