Orbital susceptibility of T-graphene: Interplay of high-order van Hove singularities and Dirac cones

Abstract

Square-octagon lattice underlies the description of a family of two-dimensional materials such as tetragraphene. In the present paper we show that the tight-binding model of square-octagon lattice contains both conventional and high-order van Hove points. In particular, the spectrum of the model contains flat lines along some directions composed of high-order saddle points. Their role is analyzed by calculating orbital susceptibility of electrons. We find that the presence of van Hove singularities of different kinds in the density of states leads to strong responses: paramagnetic for ordinary singularities and more complicated for high-order singularities. It is shown that the orbital susceptibility as a function of hoppings ratio $\alpha$ reveals the dia- to paramagnetic phase transition at $\alpha \approx 0.94$. This is due to the competition of paramagnetic contribution of high-order VHS and diamagnetic contribution of Dirac cones. The results for the tight-binding model are compared with low-energy effective pseudospin-1 model near the three band touching point.

13 pages, 5 figures

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• Orbital susceptibility of T-graphene: Interplay of high-order van Hove singularities and Dirac cones
• High-order Van Hove singularities and their connection to flat bands
• Moiré lattice effects on the orbital magnetic response of twisted bilayer graphene and Condon instability
• Charge Conservation Beyond Uniformity: Spatially Inhomogeneous Electromagnetic Response in Periodic Solids
• Detecting topological phases in the square-octagon lattice with statistical methods
• Single monkey-saddle singularity of a Fermi surface and its instabilities
• A semimetallic square-octagon (fes) two-dimensional polymer with high mobility
• An experimental scheme for determining the Berry phase in two-dimensional quantum materials with a flat band
• Differential entropy per particle as a probe of van Hove singularities and flat bands
• Visualizing near-coexistence of massless Dirac electrons and ultra-massive saddle point electrons
• Tailoring higher-order van Hove singularities in non-Hermitian interface systems via Floquet engineering
• Triplet superconductivity supported by an X${}_9$ high-order Van Hove singularity