Optical spectral weight, phase stiffness, and T c bounds for trivial and topological flat band superconductors.
Proc Natl Acad Sci U S A
; 118(34)2021 Aug 24.
Article
em En
| MEDLINE
| ID: mdl-34404730
ABSTRACT
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.
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MEDLINE
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En
Ano de publicação:
2021
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Article