Superfluidity in topologically nontrivial flat bands

By S. Peotta, P. Törmä. Nature Communications, 2015

643 citations recorded by the source corpus.

Topological invariants built from the periodic Bloch functions characterize new phases of matter, such as topological insulators and topological superconductors. The most important topological invariant is the Chern number that explains the quantized conductance of the quantum Hall effect. Here we provide a general result for the superfluid weight Ds of a multiband superconductor that is applicable to topologically nontrivial bands with nonzero Chern number C. We find that the integral over the Brillouin-zone of the quantum metric, an invariant calculated from the Bloch functions, gives the superfluid weight in a flat band, with the bound Ds⩾|C|. Thus, even a flat band can carry finite superfluid current, provided the Chern number is nonzero. As an example, we provide Ds for the time-reversal invariant attractive Harper–Hubbard model that can be experimentally tested in ultracold gases. In general, our results establish that a topologically nontrivial flat band is a promising concept for increasing the critical temperature of the superconducting transition. The critical temperature of superconductors is proportional to the particle coupling energy, but this is different to conventional superfluids where this coupling is small. Here, the authors establish a relation between superconductivity and superfluidity and the topological properties of their band structures.

Subfields: Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/8ea4d7ffb66f3fdede01b9811eb16fb2d8e0cfae

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Citations in the corpus

Superconductivity, superfluidity and quantum geometry in twisted multilayer systems (2021, background): “However, these have apparently been regarded as system-specific findings until general results connecting superfluidity with quantum geometry, such as Eqs.”
Band geometry, Berry curvature and superfluid weight (2016, background): “The importance of the quantum geometric tensor, especially in flat-band systems, has been revealed in connection with lattice fractional quantum Hall states [14,15], flat-band superfluidity [20,21], and orbital magnetic susceptibility [22,23].”
Flat bands, strange metals and the Kondo effect (2023, neutral): “6f).”
Artificial flat band systems: from lattice models to experiments (2018, neutral): “[68] Sebastiano Peotta and Päivi Törmä, “Superfluidity in topologically nontrivial flat bands,” Nat.”
Compact localized states and flat-band generators in one dimension (2016, neutral): “[29] Sebastiano Peotta and Päivi Törmä, “Superfluidity in topologically nontrivial flat bands,” Nat.”
Machine learning modeling of superconducting critical temperature (2017, background): “The associated large peak in the density of states (infinitely large in the limit of truly flat bands) can lead to strong electronic instability, and has been discussed recently as one possible way to high-temperature superconductivity.(33,34)”