Controlling charge density order in 2H-TaSe${}_2$ using a van Hove singularity

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.

main text: 12 pages, 6 figures; supplement: 25 pages, 15 figures

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