TiSe2 is a band insulator created by lattice fluctuations, not an excitonic insulator
Abstract TiSe2 is a narrow-gap insulator with a rich array of unique properties. In addition to being a superconductor under certain modifications, it is commonly thought to be a rare realisation of an excitonic insulator. Below 200 K, TiSe2 undergoes a transition from a high-symmetry ( $$P\bar{3}m1...
Saved in:
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Nature Portfolio
2025-05-01
|
| Series: | npj Computational Materials |
| Online Access: | https://doi.org/10.1038/s41524-025-01631-4 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1849688339183042560 |
|---|---|
| author | Dimitar Pashov Ross E. Larsen Matthew D. Watson Swagata Acharya Mark van Schilfgaarde |
| author_facet | Dimitar Pashov Ross E. Larsen Matthew D. Watson Swagata Acharya Mark van Schilfgaarde |
| author_sort | Dimitar Pashov |
| collection | DOAJ |
| description | Abstract TiSe2 is a narrow-gap insulator with a rich array of unique properties. In addition to being a superconductor under certain modifications, it is commonly thought to be a rare realisation of an excitonic insulator. Below 200 K, TiSe2 undergoes a transition from a high-symmetry ( $$P\bar{3}m1$$ P 3 ¯ m 1 ) phase to a low-symmetry ( $$P\bar{3}c1$$ P 3 ¯ c 1 ) charge density wave (CDW). Here we establish that it is indeed an insulator in both $$P\bar{3}m1$$ P 3 ¯ m 1 and $$P\bar{3}c1$$ P 3 ¯ c 1 phases. However, the insulating state is driven not by excitonic effects but by symmetry-breaking. In the CDW phase it is static. At high temperature, thermally driven instantaneous deviations from $$P\bar{3}m1$$ P 3 ¯ m 1 break the symmetry on the characteristic time scale of a phonon. Even though the time-averaged lattice structure assumes $$P\bar{3}m1$$ P 3 ¯ m 1 symmetry, the time-averaged energy band structure is closer to the CDW phase – a rare instance of a metal-insulator transition induced by dynamical symmetry breaking. We establish these conclusions from quasiparticle self-consistent GW (QSG W) and many-body calculations (QS $$G\widehat{W}$$ G W ̂ ), in combination with molecular dynamics simulations to capture the effects of thermal disorder. The many-body theory includes explicitly ladder diagrams in the polarizability, which incorporates excitonic effects in an ab initio manner. We find that the excitonic modification to the potential is weak, ruling out the possibility that TiSe2 is an excitonic insulator. |
| format | Article |
| id | doaj-art-e0a0e93d17ac40dabb80093c703d5e1d |
| institution | DOAJ |
| issn | 2057-3960 |
| language | English |
| publishDate | 2025-05-01 |
| publisher | Nature Portfolio |
| record_format | Article |
| series | npj Computational Materials |
| spelling | doaj-art-e0a0e93d17ac40dabb80093c703d5e1d2025-08-20T03:22:03ZengNature Portfolionpj Computational Materials2057-39602025-05-011111910.1038/s41524-025-01631-4TiSe2 is a band insulator created by lattice fluctuations, not an excitonic insulatorDimitar Pashov0Ross E. Larsen1Matthew D. Watson2Swagata Acharya3Mark van Schilfgaarde4Theory and Simulation of Condensed Matter, King’s College LondonComputational Science Center, National Renewable Energy LaboratoryDiamond Light Source Ltd, Harwell Science and Innovation CampusMaterials, Chemical and Computational Science Directorate, National Renewable Energy LaboratoryMaterials, Chemical and Computational Science Directorate, National Renewable Energy LaboratoryAbstract TiSe2 is a narrow-gap insulator with a rich array of unique properties. In addition to being a superconductor under certain modifications, it is commonly thought to be a rare realisation of an excitonic insulator. Below 200 K, TiSe2 undergoes a transition from a high-symmetry ( $$P\bar{3}m1$$ P 3 ¯ m 1 ) phase to a low-symmetry ( $$P\bar{3}c1$$ P 3 ¯ c 1 ) charge density wave (CDW). Here we establish that it is indeed an insulator in both $$P\bar{3}m1$$ P 3 ¯ m 1 and $$P\bar{3}c1$$ P 3 ¯ c 1 phases. However, the insulating state is driven not by excitonic effects but by symmetry-breaking. In the CDW phase it is static. At high temperature, thermally driven instantaneous deviations from $$P\bar{3}m1$$ P 3 ¯ m 1 break the symmetry on the characteristic time scale of a phonon. Even though the time-averaged lattice structure assumes $$P\bar{3}m1$$ P 3 ¯ m 1 symmetry, the time-averaged energy band structure is closer to the CDW phase – a rare instance of a metal-insulator transition induced by dynamical symmetry breaking. We establish these conclusions from quasiparticle self-consistent GW (QSG W) and many-body calculations (QS $$G\widehat{W}$$ G W ̂ ), in combination with molecular dynamics simulations to capture the effects of thermal disorder. The many-body theory includes explicitly ladder diagrams in the polarizability, which incorporates excitonic effects in an ab initio manner. We find that the excitonic modification to the potential is weak, ruling out the possibility that TiSe2 is an excitonic insulator.https://doi.org/10.1038/s41524-025-01631-4 |
| spellingShingle | Dimitar Pashov Ross E. Larsen Matthew D. Watson Swagata Acharya Mark van Schilfgaarde TiSe2 is a band insulator created by lattice fluctuations, not an excitonic insulator npj Computational Materials |
| title | TiSe2 is a band insulator created by lattice fluctuations, not an excitonic insulator |
| title_full | TiSe2 is a band insulator created by lattice fluctuations, not an excitonic insulator |
| title_fullStr | TiSe2 is a band insulator created by lattice fluctuations, not an excitonic insulator |
| title_full_unstemmed | TiSe2 is a band insulator created by lattice fluctuations, not an excitonic insulator |
| title_short | TiSe2 is a band insulator created by lattice fluctuations, not an excitonic insulator |
| title_sort | tise2 is a band insulator created by lattice fluctuations not an excitonic insulator |
| url | https://doi.org/10.1038/s41524-025-01631-4 |
| work_keys_str_mv | AT dimitarpashov tise2isabandinsulatorcreatedbylatticefluctuationsnotanexcitonicinsulator AT rosselarsen tise2isabandinsulatorcreatedbylatticefluctuationsnotanexcitonicinsulator AT matthewdwatson tise2isabandinsulatorcreatedbylatticefluctuationsnotanexcitonicinsulator AT swagataacharya tise2isabandinsulatorcreatedbylatticefluctuationsnotanexcitonicinsulator AT markvanschilfgaarde tise2isabandinsulatorcreatedbylatticefluctuationsnotanexcitonicinsulator |