Orbital-selective Band Hybridisation at the Charge Density Wave Transition in Monolayer TiTe${}_2$

Abstract

An anomalous $(2\times 2)$ charge density wave (CDW) phase emerges in monolayer 1T-TiTe${}_2$ which is absent for the bulk compound, and whose origin is still poorly understood. Here, we investigate the electronic band structure evolution across the CDW transition using temperature-dependent angle-resolved photoemission spectroscopy. Our study reveals an orbital-selective band hybridisation between the backfolded conduction and valence bands occurring at the CDW phase transition, which in turn leads to a significant electronic energy gain, underpinning the CDW transition. For the bulk compound, we show how this energy gain is almost completely suppressed due to the three-dimensionality of the electronic band structure, including via a $k_z$-dependent band inversion which switches the orbital character of the valence states. Our study thus sheds new light on how control of the electronic dimensionalilty can be used to trigger the emergence of new collective states in 2D materials.

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• Orbital-selective charge-density wave in TaTe${}_4$
• Lifshitz transition enabling superconducting dome around the quantum critical point in TiSe${}_2$
• Chiral charge density wave and backscattering-immune orbital texture in monolayer 1T-TiTe2
• Ab initio study of orbital-selective superconductivity in $\gamma$-BiPd