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Persistence of Charge Ordering Instability to Coulomb Engineering in the Excitonic Insulator Candidate TiSe2

Buchberger, Sebastian ; T'Veld, Yann In ; Rajan, Akhil ; Murgatroyd, Philip A.E. ; Edwards, Brendan ; Saika, Bruno K. ; Kushwaha, Naina ; Visscher, Maria H. ; Berges, Jan and Carbone, Dina LU , et al. (2025) In Physical Review X 15(4).
Abstract

TiSe2 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) TiSe2/graphite and ML TiSe2/h-BN. We observe how the modified substrate screening... (More)

TiSe2 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) TiSe2/graphite and ML TiSe2/h-BN. We observe how the modified substrate screening environment drives a renormalization of the quasiparticle band gap of the TiSe2 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 TiSe2.

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publishing date
type
Contribution to journal
publication status
published
subject
in
Physical Review X
volume
15
issue
4
article number
041028
publisher
American Physical Society
external identifiers
  • scopus:105022635456
ISSN
2160-3308
DOI
10.1103/9trc-9865
language
English
LU publication?
yes
id
f641543a-e491-4b8c-898f-5dd18feca3b6
date added to LUP
2026-02-02 11:53:26
date last changed
2026-02-02 11:54:34
@article{f641543a-e491-4b8c-898f-5dd18feca3b6,
  abstract     = {{<p>TiSe2 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) TiSe2/graphite and ML TiSe2/h-BN. We observe how the modified substrate screening environment drives a renormalization of the quasiparticle band gap of the TiSe2 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 TiSe2.</p>}},
  author       = {{Buchberger, Sebastian and T'Veld, Yann In and Rajan, Akhil and Murgatroyd, Philip A.E. and Edwards, Brendan and Saika, Bruno K. and Kushwaha, Naina and Visscher, Maria H. and Berges, Jan and Carbone, Dina and Osiecki, Jacek and Polley, Craig and Wehling, Tim and King, Phil D.C.}},
  issn         = {{2160-3308}},
  language     = {{eng}},
  number       = {{4}},
  publisher    = {{American Physical Society}},
  series       = {{Physical Review X}},
  title        = {{Persistence of Charge Ordering Instability to Coulomb Engineering in the Excitonic Insulator Candidate TiSe2}},
  url          = {{http://dx.doi.org/10.1103/9trc-9865}},
  doi          = {{10.1103/9trc-9865}},
  volume       = {{15}},
  year         = {{2025}},
}