Year: 2026
Type: preprint
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.
Source: arXiv (Cornell University)
Language: English
Subfield: Condensed Matter Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, U.S. Department of Energy, Gordon and Betty Moore Foundation, University of Michigan, Center for Integrated Nanotechnologies, Office of Science, National Nuclear Security Administration, Multidisciplinary University Research Initiative, Office of Naval Research, Division of Materials Research, Laboratory Directed Research and Development
Awards: G1017065088, G1461635341, G1527848044, G2356915424, G2821339390, G3094441217, MRSEC: Center for Materials Innovations at Michigan, G3874738311, G5498603677, G556563932, G560771542, Creating Hybrid States of Matter for Topological Quantum Computing, G6098521345, G6410514744, G6482216908, G6563880843, G70659677, G7420434293, G7631180099, G7977574923, G8515682721, G8876996369, G91514826
OpenAlex ID: W7211871622