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arXiv · 2606.01235

Interplay between Quantum Metric and Hybridized Collective Mode in Flat-Band Superfluids

Yi Liu·Mingyan Wang·Penghui Hu·Yao Lu
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Abstract

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 ($\omega \propto q^2$) at small momenta. We show that the dispersion coefficients of this collective mode are governed by the normal-state quantum metric of the flat band. These analytical predictions are in excellent agreement with numerical calculations. Our results are applicable to any generic $s$-wave flat-band superfluid, provided the flat band is energetically well separated from other dispersive bands.

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Yi Liu, Mingyan Wang, Penghui Hu, Yao Lu. 2026-05-31. Interplay between Quantum Metric and Hybridized Collective Mode in Flat-Band Superfluids. https://arxiv.org/abs/2606.01235

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