Exotic charge density waves and superconductivity on the Kagome Lattice

TL;DR

This paper investigates charge density waves, superconductivity, and nematicity in kagome lattice materials, revealing how Coulomb interactions influence various electronic orders and their experimental implications.

Contribution

It provides a comprehensive analysis of charge instabilities and emergent orders in the spinless kagome lattice with Coulomb interactions at van Hove filling, highlighting the role of bond charge and loop current orders.

Findings

Bond charge orders are enhanced at nesting vectors due to sublattice texture.

Next nearest-neighbor Coulomb repulsion favors 2x2 loop current order.

Increasing interactions leads to a nematic state breaking C6 symmetry.

Abstract

Recent experiments have identified fascinating electronic orders in kagome materials, including intriguing superconductivity, charge density wave (CDW) and nematicity. In particular, some experimental evidence for AV$_3$Sb$_5$ (A = K,Rb,Cs) and related kagome metals hints at the formation of orbital currents in the charge density wave ordered regime, providing a mechanism for spontaneous time-reversal symmetry breaking in the absence of local moments. In this work, we comprehensively explore the competitive charge instabilities of the spinless kagome lattice with inter-site Coulomb interactions at the pure-sublattice van Hove filling. From the analysis of the charge susceptibility, we find that, at the nesting vectors, while the onsite charge order is dramatically suppressed, the bond charge orders are substantially enhanced owing to the sublattice texture on the hexagonal Fermi surface. Furthermore, we demonstrate that nearest-neighbor and next nearest-neighbor bonds are characterized by significant intrinsic real and imaginary bond fluctuations, respectively. The 2$\times$2 loop current order is thus favored by the next nearest-neighbor Coulomb repulsion. Interestingly, increasing interactions further leads to a nematic state with intra-cell sublattice density modulation that breaks the $C_6$ rotational symmetry. We further explore superconducting orders descending from onsite and bond charge fluctuations, and discuss our model's implications on the experimental status quo.