Controlling charge density order in 2H-TaSe$_{2}$ using a van Hove singularity

TL;DR

This study explores how tuning the Fermi level near a van Hove singularity in 2H-TaSe$_{2}$ can control the charge density wave order, revealing a transition from a $(3 imes 3)$ to a $(2 imes 2)$ superlattice.

Contribution

It demonstrates the manipulation of charge density wave periodicity via surface doping and theoretical modeling of the Lifshitz transition's impact on charge order.

Findings

Disappearance of the $(3\times 3)$ charge density wave at high doping.

Formation of a $(2\times 2)$ superlattice due to van Hove singularity.

Coupling between Lifshitz transition and charge density order explained by models.

Abstract

We report on the interplay between a van Hove singularity and a charge density wave state in 2H-TaSe$_{2}$. We use angle-resolved photoemission spectroscopy to investigate changes in the Fermi surface of this material under surface doping with potassium. At high doping, we observe modifications which imply the disappearance of the $(3\times 3)$ charge density wave and formation of a different correlated state. Using a tight-binding-based approach as well as an effective model, we explain our observations as a consequence of coupling between the single-particle Lifshitz transition during which the Fermi level passes a van Hove singularity and the charge density order. In this scenario, the high electronic density of states associated with the van Hove singularity induces a change in the periodicity of the charge density wave from the known $(3\times 3)$ to a new $(2\times 2)$ superlattice.