Persistence of charge ordering instability to Coulomb engineering in the excitonic insulator candidate TiSe${}_2$

Abstract

TiSe${}_2$ has long been considered one of the best candidate materials to host the elusive excitonic insulator (EI) phase. However, a finite coupling to the lattice can generically be expected, while a lack of "smoking-gun" signatures for the importance of the electron-hole interaction in driving the phase transition has rendered it challenging to distinguish the EI from the conventional charge-density-wave (CDW) phase. Here, we demonstrate a new approach, exploiting the susceptibility of excitons to dielectric screening. We combine mechanical exfoliation with molecular-beam epitaxy to fabricate ultra-clean van der Waals heterostructures of monolayer (ML-)TiSe${}_2$/graphite and ML-TiSe${}_2$/hBN. We observe how the modified substrate screening environment drives a renormalisation of the quasi-particle band gap of the TiSe${}_2$ layer, signifying its susceptibility to Coloumb engineering. The temperature-dependent evolution of its electronic structure, however, remains unaffected, indicating that excitons are not required to drive the CDW transition in TiSe${}_2$.

15 pages including supplemental information, 5+4 figures

References in corpus (23)

• Observation of giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor
• Probing Excitonic Dark States in Single-layer Tungsten Disulfide
• Evidence for an excitonic insulator phase in 1T-TiSe${}_2$
• Controlling many-body states by the electric-field effect in a two-dimensional material
• Excitons versus electron-hole plasma in monolayer transition metal dichalcogenide semiconductors
• Evidence for equilibrium excitons and exciton condensation in monolayer WTe2
• Renormalization of quasiparticle band gap in doped two-dimensional materials from many-body calculations
• Revealing the role of electrons and phonons in the ultrafast recovery of charge density wave correlations in 1$T$-TiSe${}_2$
• Dielectric permittivity, conductivity and breakdown field of hexagonal boron nitride
• Evidences for the exciton gas phase and its condensation in monolayer 1T-ZrTe2
• Morphology Control of Epitaxial Monolayer Transition Metal Dichalcogenides
• Evidence of high-temperature exciton condensation in a two-dimensional semimetal
• Random Phase Approximation for gapped systems: role of vertex corrections and applicability of the constrained random phase approximation
• Role of electron-phonon coupling in excitonic insulator candidate Ta2NiSe5
• Phonon Self-Energy Corrections: To Screen, or Not to Screen
• Dramatic Plasmon Response to the Charge-Density-Wave Gap Development in $1\text{T}-{\mathrm{TiSe}}_2$
• Enhancing charge-density-wave order in 1T-TiSe2 nanosheet by encapsulation with hexagonal Boron Nitride
• Observation of possible excitonic charge density waves and metal-insulator transitions in atomically thin semimetals
• Evidence for an Excitonic Insulator State in Ta${}_2$Pd${}_3$Te${}_5$
• Lattice fluctuations, not excitonic correlations, mediated electronic localization in TiSe${}_2$
• Ab initio electron-lattice downfolding: potential energy landscapes, anharmonicity, and molecular dynamics in charge density wave materials
• Molecular Beam Epitaxy growth of MoTe${}_2$ on Hexagonal Boron Nitride
• Quasiparticle gap renormalization driven by internal and external screening in a WS${}_2$ device

Cited by in corpus (1)

• Electron-phonon-dominated charge-density-wave fluctuations in TiSe${}_2$ accessed by ultrafast nonequilibrium dynamics