Persistence of Charge Ordering Instability to Coulomb Engineering in the Excitonic Insulator Candidate TiSe 2

Year: 2025

Type: article

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 ultraclean van der Waals heterostructures of monolayer (ML) TiSe 2 /graphite and ML TiSe 2 / h -BN. We observe how the modified substrate screening environment drives a renormalization of the quasiparticle band gap of the TiSe 2 layer, signifying its susceptibility to Coulomb 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 .

Source: Physical Review X

DOI: 10.1103/9trc-9865

Authors: Sebastian Buchberger, Yann in ’t Veld, Akhil Rajan, Philip A. E. Murgatroyd, Brendan Edwards, Bruno K. Saika, Naina Kushwaha, Maria H. Visscher, Jan Berges, Dina Carbone, Jacek Osiecki, Craig Polley, Tim Wehling, Phil D. C. King

Institutions: University of St Andrews, Max Planck Institute for Chemical Physics of Solids, Universität Hamburg, Research Complex at Harwell, Central Laser Facility, University of Bremen, Lund University, MAX IV Laboratory, Hamburg Centre for Ultrafast Imaging

Language: English

Topic: 2D Materials and Applications

Subfield: Materials Chemistry

Field: Materials Science

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $4,200

Funders: Leverhulme Trust, Deutsche Forschungsgemeinschaft, VINNOVA, Svenska Forskningsrådet Formas, Vetenskapsrådet, Universität Bremen, Engineering and Physical Sciences Research Council

OpenAlex ID: W4416204986