Optical spectral weight, phase stiffness, and T c bounds for trivial and topological flat band superconductors.

Autor:	Verma N; Department of Physics, The Ohio State University, Columbus, OH 43210., Hazra T; Department of Physics, The Ohio State University, Columbus, OH 43210.; Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854., Randeria M; Department of Physics, The Ohio State University, Columbus, OH 43210; randeria.1@osu.edu.
Jazyk:	angličtina
Zdroj:	Proceedings of the National Academy of Sciences of the United States of America [Proc Natl Acad Sci U S A] 2021 Aug 24; Vol. 118 (34).
DOI:	10.1073/pnas.2106744118
Abstrakt:	We present exact results that give insight into how interactions lead to transport and superconductivity in a flat band where the electrons have no kinetic energy. We obtain bounds for the optical spectral weight for flat-band superconductors that lead to upper bounds for the superfluid stiffness and the two-dimensional (2D) [Formula: see text] We focus on on-site attraction [Formula: see text] on the Lieb lattice with trivial flat bands and on the π-flux model with topological flat bands. For trivial flat bands, the low-energy optical spectral weight [Formula: see text] with [Formula: see text] , where n is the flat-band density and Ω is the Marzari-Vanderbilt spread of the Wannier functions (WFs). We also obtain a lower bound involving the quantum metric. For topological flat bands, with an obstruction to localized WFs respecting all symmetries, we again obtain an upper bound for [Formula: see text] linear in [Formula: see text] We discuss the insights obtained from our bounds by comparing them with mean-field and quantum Monte Carlo results. Competing Interests: The authors declare no competing interest.
Databáze:	MEDLINE
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