Interlayer Exciton Condensate Stiffness Is Non-Monotonic in Quantum Metric
Abstract
Identifying the origin of the superfluid stiffness of electron-electron and electron-hole pair condensates is an important issue in flat-band physics. Here, we study the stiffness of bilayer exciton condensates using exact diagonalization and realistic Coulomb interactions across a wide variety of flat Chern band systems, including Landau levels, mixed Landau levels, and moiré bands. We find that stiffness is non-monotonic in the trace of the quantum metric and that it develops peaks when the band wavefunctions are engineered to be similar to those of Landau levels. The stiffness predicted by mean-field theory agrees quantitatively with exact diagonalization in these optimal cases, but systematically overestimates it otherwise. Flat bands with identical quantum geometry tensors can exhibit substantial differences in stiffness. The stiffness of condensates formed between moiré flat bands, which typically have strong variations in Berry curvature and quantum metric across their Brillouin zones, tends to be larger when the bands have non-zero Chern numbers and can be larger than that of Landau levels. Our results reveal a behavior that is richer than that suggested by simple geometric bounds and provide new guiding principles for the design of robust flat-band condensates with large superfluid stiffness.
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BibTeX
@misc{zou2026interlayer,
title = {{Interlayer Exciton Condensate Stiffness Is Non-Monotonic in Quantum Metric}},
author = {Bo Zou and Yitong Zhang and Siddhartha Sarkar and Shi-Zeng Lin and Allan H. MacDonald and Kai Sun},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.04729},
eprint = {2609.04729},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.04729},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - Interlayer Exciton Condensate Stiffness Is Non-Monotonic in Quantum Metric
AU - Bo Zou
AU - Yitong Zhang
AU - Siddhartha Sarkar
AU - Shi-Zeng Lin
AU - Allan H. MacDonald
AU - Kai Sun
PY - 2026
DA - 2026/09/04
PB - arXiv
DO - 10.48550/arxiv.2609.04729
UR - https://arxiv.org/abs/2609.04729
AB - Identifying the origin of the superfluid stiffness of electron-electron and electron-hole pair condensates is an important issue in flat-band physics. Here, we study the stiffness of bilayer exciton condensates using exact diagonalization and realistic Coulomb interactions across a wide variety of flat Chern band systems, including Landau levels, mixed Landau levels, and moiré bands. We find that stiffness is non-monotonic in the trace of the quantum metric and that it develops peaks when the band wavefunctions are engineered to be similar to those of Landau levels. The stiffness predicted by mean-field theory agrees quantitatively with exact diagonalization in these optimal cases, but systematically overestimates it otherwise. Flat bands with identical quantum geometry tensors can exhibit substantial differences in stiffness. The stiffness of condensates formed between moiré flat bands, which typically have strong variations in Berry curvature and quantum metric across their Brillouin zones, tends to be larger when the bands have non-zero Chern numbers and can be larger than that of Landau levels. Our results reveal a behavior that is richer than that suggested by simple geometric bounds and provide new guiding principles for the design of robust flat-band condensates with large superfluid stiffness.
ER -