Flat-band superconductivity for tight-binding electrons on a square-octagon lattice

Nunes, Lizardo H.C.M.; Smith, C. Morais

doi:10.1103/physrevb.101.224514

Cited by 35 publications

(22 citation statements)

References 62 publications

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“…Moreover, a square-octagon lattice was theoretically studied. Two perfectly flat bands were found [9] and the calculated superconducting phase diagram was found to have two superconducting domes [9], as observed in several types of unconventional superconductors. Thus, there is a resurgence of interest from the experimental front in flat bands as a means to explore unconventional superconductivity [8,19,20].…”

Section: Introductionsupporting

confidence: 66%

“…This band structure reveals a pair of Dirac points similar to those found in graphene, and a dispersionless, flat band that originates from the kinetic frustration associated with the geometry of the kagome lattice. Flat bands are exciting because the associated high density of electronic states hints at possible correlated electronic phases when found close to the Fermi level [8][9][10]. The possibility of accessing flat bands and their influence on the physical properties of the system has been studied for about three decades [10][11][12][13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

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Nodeless kagome superconductivity in LaRu3Si2

Mielke

Qin

Yin

et al. 2021

Phys. Rev. Materials

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We report muon spin rotation (μSR) experiments together with first-principles calculations on microscopic properties of superconductivity in the kagome superconductor LaRu 3 Si 2 with T c 7K. Below T c , μSR reveals type-II superconductivity with a single s-wave gap, which is robust against hydrostatic pressure up to 2 GPa. We find that the calculated normal state band structure features a kagome flat band, and Dirac as well as van Hove points formed by the Ru-dz 2 orbitals near the Fermi level. We also find that electron-phonon coupling alone can only reproduce a small fraction of T c from calculations, which suggests other factors in enhancing T c such as the correlation effect from the kagome flat band, the van Hove point on the kagome lattice, and the high density of states from narrow kagome bands. Our experiments and calculations taken together point to nodeless moderate coupling kagome superconductivity in LaRu 3 Si 2 .

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Section: Introductionsupporting

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Nodeless kagome superconductivity in LaRu3Si2

Mielke

Qin

Yin

et al. 2021

Phys. Rev. Materials

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“…Most analysis on two-dimensional systems with flat bands exploit mean field approximations [25][26][27] but there are questions here on the validity of a conventional BCS treatment in a flat band, as the interaction strength dominates the dynamics resulting in strongly correlated phases even for weak interactions. A full quantum treatment for fermions in one-dimensional flat band systems has also been explored [43,44], but usually only in the isolated flat band approximation where it has been shown that the ground state can coincide with the BCS ground state [44].…”

Section: Many-body Correlations At Half-fillingmentioning

confidence: 99%

“…1(c), the Lieb lattice has a flat energy band that touches a dispersive band at a single k-point, which becomes a Dirac cone [20] for uniform onsite energies. Dispersionless (or flat) single particle energy bands arise through a destructive interference effect of the single particle wavefunction, [21][22][23][24][25][26][27], leading to an infinite energy degeneracy and means that conventional [13]. The incoming solid red laser (for VA) is polarised along the y-direction, while the dashed patterned laser (for VB) is polarised in the direction orthogonal to the x-y plane.…”

Section: Introductionmentioning

confidence: 99%

Hubbard models and state preparation in an optical Lieb lattice

Flannigan,

Madail,

Dias

et al. 2021

Preprint

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Inspired by the growing interest in probing many-body phases in novel two-dimensional lattice geometries we investigate the properties of cold atoms as they could be observed in an optical Lieb lattice. We begin by computing Wannier functions localised at individual sites for a realistic experimental setup, and determining coefficients for a Hubbard-like model. Based on this, we show how experiments could probe the robustness of edge states in a Lieb lattice with diagonal boundary conditions to the effects of interactions and realise strongly correlated many-body phases in this geometry. We then generalise this to interacting particles in a half-filled 1D Lieb ladder, where excitations are dominated by flat band states. We show that for strong attractive interactions, pair correlations are enhanced even when there is strong mixing with the Dirac cone. These findings in 1D raise interesting questions about the phases in the full 2D Lieb lattice which we show can be explored in current experiments.

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“…Also, by using the novel band structure engineering technique, so-called twistronics, many nearly flat band systems have been realized in various Moire superlattice systems composed of misaligned two-dimensional layers, such as the twisted bilayer graphene [36][37][38][39][40][41][42], twisted bilayer transition metal dichalcogenides [43,44], and twisted multi-layer silicene [45]. In particular, the twisted bilayer graphene at the magic angle [46] has attracted a great attention due to its unconventional superconductivity [36,[47][48][49][50][51][52][53][54][55][56][57] and Mott insulating phases [36]. Furthermore, in artificial systems, such as the photonic lattices [58][59][60][61][62][63][64][65][66][67][68][69][70][71], cold atom systems [72,73], engineered atomic lattices [74], and metamaterials [75][76][77]…”

Section: Introductionmentioning

confidence: 99%

Singular flat bands

Rhim

Yang

2021

Advances in Physics: X

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We review recent progresses in the study of flat band systems, especially focusing on the fundamental physics related to the singularity of the flat band's Bloch wave functions. We first explain that the flat bands can be classified into two classes: singular and non-singular flat bands, based on the presence or absence of the singularity in the flat band's Bloch wave functions. The singularity is generated by the band crossing of the flat band with another dispersive band. In the singular flat band, one can find a special kind of eigenmodes, called the non-contractible loop states and the robust boundary modes, which exhibit nontrivial real-space topology. Then, we review the experimental realization of these topological eigenmodes of the flat band in the photonic lattices. While the singularity of the flat band is topologically trivial, we show that the maximum quantum distance around the singularity is a bulk invariant representing the strength of the singularity which protects the robust boundary modes. Finally, we discuss how the maximum quantum distance or the strength of the singularity manifests itself in the anomalous Landau level spreading of the singular flat band when it has a quadratic band-crossing with another band. Si ng ul ar fla t ba nd Non-contractible loop states Anomalous Landau levels

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Flat-band superconductivity for tight-binding electrons on a square-octagon lattice

Cited by 35 publications

References 62 publications

Nodeless kagome superconductivity in LaRu3Si2

Nodeless kagome superconductivity in LaRu3Si2

Hubbard models and state preparation in an optical Lieb lattice

Singular flat bands

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