Peotta, Sebastiano

Date: Tuesday, June 16, 2015
Time: 16:00
Place: ETH Zurich, Hönggerberg, HPF G 6
Host: Päivi Törmä/Tilman Esslinger

Superfluidity in topoligically nontrivial flat bands

Sebastiano Peotta
Aalto University, Finnland

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 expression for the superfluid weight D_s of a multiband superconductor that is applicable to topologically nontrivial bands with nonzero Chern number C. We find a new invariant calculated from the Bloch functions that gives the superfluid weight in a flat band, with the bound D_s ≥ |C|. Thus, even a flat band can carry finite superfluid current, provided the Chern number is non-zero. As an example, we provide D_s 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 route towards room-temperature superconductivity.

References: arXiv:1506.02815