High-order van Hove singularities and nematic instability in the kagome superconductor CsTi$_3$Bi$_5$

TL;DR

This paper investigates the electronic structure of CsTi$_3$Bi$_5$, revealing high-order van Hove singularities that promote nematicity and superconductivity, and demonstrates the robustness of its superconducting properties under various conditions.

Contribution

It identifies high-order van Hove singularities in CsTi$_3$Bi$_5$ and analyzes their role in nematicity and superconductivity, providing insights into non-translational symmetry-breaking states in kagome metals.

Findings

High-order van Hove singularities are present in CsTi$_3$Bi$_5$.

VHSs enhance electronic correlations and nematicity.

Superconductivity remains robust under doping and surface modifications.

Abstract

ATi$_3$Bi$_5$ (A = Cs or Rb) are emerging topological kagome metals that exhibit superconductivity and nematicity without intertwining translational symmetry-breaking charge orders. In this work, we explore the fermiology of their titanium kagome electrons and identify a set of sublattice-pure, high-order van Hove singularities (VHSs) that can suppress charge ordering and enhance electronic correlations and superconductivity. Our calculations of charge susceptibility for kagome bands with both normal and high-order VHSs emphasize the role of these VHSs in driving electronic nematicity in CsTi$_3$Bi$_5$. Additionally, we compute the phonon spectrum and electron-phonon interactions for CsTi$_3$Bi$_5$ under pristine, doped, and kagome-exposed surface conditions, revealing its robustness against structural instabilities while enhancing the superconducting transition temperature. Our work positions ATi$_3$Bi$_5$ as a key platform for investigating superconductivity and electronic nematicity without translational symmetry-breaking states in kagome metals.