Electronic instabilities of kagome metals: Saddle points and Landau theory

Park, Takamori; Ye, Mengxing; Balents, Leon

doi:10.1103/physrevb.104.035142

Cited by 213 publications

(191 citation statements)

References 58 publications

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“…The observation of electronic chiral charge order is unprecedented in the studying of quantum materials, and can be highly related to the electronic nature of kagome lattice at van Hove filling as in AV 3 Sb 5 [42][43][44][45][46]. In contrast to the honeycomb lattice, the kagome lattice has three sublattices, and the kagome lattice at van Hove filling exhibits unequal predominant sublattice occupancy [42].…”

Section: Discussionmentioning

confidence: 99%

“…Phenomenologically, a chiral charge order parameter has also been proposed to interact with the underlying topological band structure of this material to produce a large intrinsic anomalous Hall effect [28,[43][44][45], which is consistent with the transport data. Another anomalous feature of the chiral charge order is that it can carry orbital currents [28,43,44,46], analogous to the fundamental Haldane model [47] and Varma model [48]. A tantalizing visualization of the orbital magnetism is recently reported by muon spin spectroscopy, and a spontaneous internal magnetic field is observed just below the charge ordering temperature [49].…”

Section: Discussionmentioning

confidence: 99%

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Electronic nature of chiral charge order in the kagome superconductor CsV3Sb5

et al. 2021

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Kagome superconductors with T C up to 7 K have been discovered for over 40 y. Recently, unconventional chiral charge order has been reported in kagome superconductor KV 3 Sb 5 , with an ordering temperature of one order of magnitude higher than the T C . However, the chirality of the charge order has not been reported in the cousin kagome superconductor CsV 3 Sb 5 , and the electronic nature of the chirality remains elusive. In this paper, we report the observation of electronic chiral charge order in CsV 3 Sb 5 via scanning tunneling microscopy (STM). We observe a 2 × 2 charge modulation and a 1 × 4 superlattice in both topographic data and tunneling spectroscopy. 2 × 2 charge modulation is highly anticipated as a charge order by fundamental kagome lattice models at van Hove filling, and is shown to exhibit intrinsic chirality. We find that the 1 × 4 superlattices form various small domain walls, and can be a surface effect as supported by our first-principles calculations. Crucially, we find that the amplitude of the energy gap opened by the charge order exhibits real-space modulations, and features 2 × 2 wave vectors with chirality, highlighting the electronic nature of the chiral charge order. STM study at 0.4 K reveals a superconducting energy gap with a gap size 2 = 0.85 meV, which estimates a moderate superconductivity coupling strength with 2 /k B T C = 3.9. When further applying a c-axis magnetic field, vortex core bound states are observed within this gap, indicative of clean-limit superconductivity.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Electronic nature of chiral charge order in the kagome superconductor CsV3Sb5

et al. 2021

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“…A CDW can be envisaged in a compressed structure too, but it is no longer a global energy minimum, because Sb2 displacements stabilizing the three-dimensional CDW are suppressed. Recent spectroscopy experiments hint at the CDW gap opening around M [7,45], in accord with theoretical studies that discuss saddle points of the kagome bands as the microscopic reason for the CDW formation [18,38]. However, it is Sb atoms that decide whether the CDW state eventually forms or not.…”

Section: Discussionmentioning

confidence: 63%

“…For example, full structural relaxation results in the unit cell volume V = 237.7 Å 3 and c/a = 1.675 with the PBE functional or V = 240.8 Å 3 and c/a = 1.715 with the D3 correction [36], to be compared with the experimental structural parameters V = 243.4 Å 3 and c/a = 1.694 at ambient pressure [5]. The proximity of the saddle points to the Fermi level is deemed crucial for the electronic instability and CDW formation [19,37,38]. Using experimental structural parameters eliminates any ambiguity in the positioning of these saddle points relative to E F .…”

Section: Methodsmentioning

confidence: 99%

Role of Sb in the superconducting kagome metal CsV$_3$Sb$_5$ revealed by its anisotropic compression

Tsirlin¹,

Fertey²,

Ortiz³

et al. 2022

SciPost Phys.

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Pressure evolution of the superconducting kagome metal CsV_33Sb_55 is studied with single-crystal x-ray diffraction and density-functional band-structure calculations. A highly anisotropic compression observed up to 5 GPa is ascribed to the fast shrinkage of the Cs–Sb distances and suppression of Cs rattling motion. This prevents Sb displacements required to stabilize the three-dimensional charge-density-wave (CDW) order and elucidates the disappearance of the CDW already at 2 GPa despite only minor changes in the electronic structure of the normal state. At higher pressures, vanadium bands still change only marginally, whereas antimony bands undergo a major reconstruction caused by the gradual formation of the interlayer Sb–Sb bonds. Our results exclude pressure tuning of vanadium kagome bands as the main mechanism for the non-trivial evolution of superconductivity in real-world kagome metals. Concurrently, we establish the central role of Sb atoms in the stabilization of a three-dimensional CDW and Fermi surface reconstruction.

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“…Given that phonons appear unable to account for the measured T c [50,73] and yet the materials appear to be weakly correlated, we propose that our mechanism might provide a partial explanation for superconductivity in kagome metals, in contrast to existing theoretical proposals which attribute superconductivity to the effects of nesting or competing density wave order [83][84][85]. In this interpretation, superconductivity originates from the Dirac-like Fermi surfaces and is not directly related to the observed charge density wave (CDW) order [75], which is potentially due to the nested portions of the band structure near the Fermi level.…”

Section: Discussionmentioning

confidence: 67%

Higher-order topological superconductivity from repulsive interactions in kagome and honeycomb systems

Geier

Ingham

et al. 2021

2D Mater.

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We discuss a pairing mechanism in interacting two-dimensional multipartite lattices that intrinsically leads to a second order topological superconducting state with a spatially modulated gap. When the chemical potential is close to Dirac points, oppositely moving electrons on the Fermi surface undergo an interference phenomenon in which the Berry phase converts a repulsive electron-electron interaction into an effective attraction. The topology of the superconducting phase manifests as gapped edge modes in the quasiparticle spectrum and Majorana Kramers pairs at the corners. We present symmetry arguments which constrain the possible form of the electron-electron interactions in these systems and classify the possible superconducting phases which result. Exact diagonalization of the Bogoliubov-de Gennes Hamiltonian confirms the existence of gapped edge states and Majorana corner states, which strongly depend on the spatial structure of the gap. Possible applications to vanadium-based superconducting kagome metals AV$_3$Sb$_3$ (A=K,Rb,Cs) are discussed.

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Electronic instabilities of kagome metals: Saddle points and Landau theory

Cited by 213 publications

References 58 publications

Electronic nature of chiral charge order in the kagome superconductor CsV3Sb5

Electronic nature of chiral charge order in the kagome superconductor CsV3Sb5

Role of Sb in the superconducting kagome metal CsV$_3$Sb$_5$ revealed by its anisotropic compression

Higher-order topological superconductivity from repulsive interactions in kagome and honeycomb systems

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