Reentrant Fulde-Ferrell-Larkin-Ovchinnikov superfluidity in the honeycomb lattice

Abstract

We study superconducting properties of population-imbalanced ultracold Fermi mixtures in the honeycomb lattice that can be effectively described by the spin-imbalanced attractive Hubbard model in the presence of a Zeeman magnetic field. We use the mean-field theory approach to obtain ground state phase diagrams including the unconventional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, which is characterized by atypical behavior of the Cooper pairs total momentum. We show that the momentum changes its value as well as direction with change of the system parameters. We discuss the influence of van Hove singularities on the possibility of the reentrant FFLO phase occurrence, without a BCS precursor.

Superfluid stiffness for the attractive Hubbard model on a honeycomb optical lattice

“…For instance, we find that the critical interaction threshold U c /t ≈ {2.23, 2.19, 2.06, 1.71} decreases with t /t = {0, −0.1, −0.2, −0.3} for the semi-metal to SF phase transition at half filling. These are consistent with the known results in the literature where U c /t ≈ {2.24, 2.13} for t /t = {0, −0.15} [15,23]. We emphasize that, in contrast to the normal to SF transition boundary, our vacuum, insulator and semi-metal to SF transition boundaries are very accurate as T BKT /t vanish quite rapidly near U c .…”

Spin-imbalanced Fermi superfluidity in a Hubbard model on a Lieb lattice

“…Since the FS of a Fermi gas in a square or cubic lattice loses its isotropy and has a square-like shape in two dimensions, especially close to Van Hove singularities, it facilitates the FFLO pairing due to a nesting effect [11], in which the pairing takes place where the FSs, shifted by the momentum q, match. Therefore, relatively significant regions with non-uniform superfluidity have been found theoretically, both with the FF [28][29][30][31][32] and the LO [33] ansatz. In the repulsive Hubbard model, superfluidity may coexist with the magnetic stripe order as found by iPEPS [34] and DMFT methods [35], or with Pomeranchuk instability as in Refs.…”

Superconductivity of KFe2As2 Under Pressure: Ab Initio Study of Tetragonal and Collapsed Tetragonal Phases

“…Theoretical calculations for the multi-band superconductors show that the change of the character of the electrons from 3D to 2D behavior (which can be observed as a modification of a shape of the Fermi surface, e.g., from cilidricallike to spherical-like) leads to a stabilization of the superconductivity [95][96][97] due to the emergence of the narrow bands [98]. In such a case, the van Hove singularity plays an important role in tuning of the superconductivity [99,100]. The manifestation of this behavior is, for instance, an appearance of the superconducting phase in the magicangle graphene superlattices [101,102], width-dependence of T c of nanofilms [103,104], or room-T c (under external pressure) hydride superconductors [105,106].…”