Spin-Imbalanced Pairing and Fermi Surface Deformation in Flat Bands

We study the attractive Hubbard model with spin imbalance on two lattices featuring a flat band: the Lieb and kagome lattices. We present mean-field phase diagrams featuring exotic superfluid phases, similar to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, whose stability is confirmed by dynamical mean-field theory (DMFT). The nature of the pairing is found to be qualitatively different from the Fermi surface shift responsible for the usual FFLO state. The presence of a flat band allows for changes in the particle momentum distributions at null energy cost. This facilitates formation of nontrivial superfluid phases via multiband Cooper pair formation: the momentum distribution of the spin component in the flat band deforms to mimic the Fermi surface of the other spin component residing in a dispersive band. The Fermi surface of the unpaired particles that are typical for gapless superfluids becomes deformed as well. The results highlight the profound effect of flat dispersions on Fermi surface instabilities, and provide a potential route for observing spin-imbalanced superfluidity and supercondutivity.

Description

| openaire: EC/H2020/702281/EU//FLATOPS

Keywords

Condensed Matter - Quantum Gases, Condensed Matter - Superconductivity

DOI

10.1103/PhysRevB.97.214503

Citation

Huhtinen, K-E, Tylutki, M, Kumar, P, Vanhala, T I, Peotta, S & Törmä, P 2018, ' Spin-Imbalanced Pairing and Fermi Surface Deformation in Flat Bands ', Physical Review B, vol. 97, no. 21, 214503, pp. 1-8 . https://doi.org/10.1103/PhysRevB.97.214503

Permanent link to this item

https://urn.fi/URN:NBN:fi:aalto-201808014144

Collections

[article-cris] Perustieteiden korkeakoulu / SCI

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