Low temperature phase transitions under CDW state in kagome metals AV3Sb5 (A=Cs,Rb,K): Significance of mix-type Fermi surface electron correlations

TL;DR

This paper investigates the multistage phase transitions in kagome metals with CDW states, emphasizing the role of mix-type Fermi surfaces and revealing mechanisms behind nematic and non-nematic orders.

Contribution

It introduces a theoretical framework explaining how mix-type Fermi surfaces influence phase transitions and predicts observable fluctuations in kagome metals.

Findings

Identification of uniform bond order caused by paramagnon interference

Prediction of E2g-symmetry nematic order with arbitrary director rotation

Detection of A1g-symmetry non-nematic order affecting lattice constants

Abstract

To understand the multistage phase transitions in V-based kagome metals inside the charge-density-wave (CDW) phase, we focus on the impact of the "mix-type" Fermi surface because it is intact in the CDW state on the "pure-type" Fermi surface. On the mixed-type Fermi surface, moderate spin correlations develop, and we reveal that uniform (q=0) bond order is caused by the paramagnon interference mechanism, which is described by the Aslamazov-Larkin vertex correction. A dominant solution is the E2g-symmetry nematic order, in which the director can be rotated arbitrarily. In addition, we obtain the A1g-symmetry non-nematic order, which leads to the change in the lattice constants without symmetry breaking. The predicted E2g and A1g channel fluctuations at q=0 can be observed by the elastoresistance measurements. These results are useful to understand the multistage phase transitions inside the 2 $\times$ 2 CDW phase. The present theory has a general significance because mix-type band structure universally exists in various kagome lattice models.