Enhanced nematicity emerging from higher-order Van Hove singularities

Motivated by the experimental identification of a higher-order Van Hove singularity (VHS) in AV3Sb5 kagome metals, we study electronic instabilities of two-dimensional lattice models with higher-order VHS and flavor degeneracy. In contrast to conventional VHSs, the larger power-law density of states and the weaker nesting propensity of higher-order VHSs conspire together to generate distinct competing instabilities. After discussing the occurrence of higher-order VHSs on square and kagome lattice models, we perform unbiased renormalization group calculations to study competing instabilities and find a rich phase diagram containing ferromagnetism, antiferromagnetism, superconductivity, and Pomeranchuk orders. Remarkably, there is a generic transition from superconductivity to a d-wave Pomeranchuk order with increasing flavor number. Implications for the intriguing quantum states of AV3Sb5 kagome metals are also discussed.