Zero-gap semiconductor to excitonic insulator transition in Ta2NiSe5
MetadataShow full item record
The excitonic insulator is a long conjectured correlated electron phase of narrow-gap semiconductors and semimetals, driven by weakly screened electron–hole interactions. Having been proposed more than 50 years ago, conclusive experimental evidence for its existence remains elusive. Ta2NiSe5 is a narrow-gap semiconductor with a small one-electron bandgap EG of <50 meV. Below TC=326 K, a putative excitonic insulator is stabilized. Here we report an optical excitation gap Eop ∼0.16 eV below TC comparable to the estimated exciton binding energy EB. Specific heat measurements show the entropy associated with the transition being consistent with a primarily electronic origin. To further explore this physics, we map the TC–EG phase diagram tuning EG via chemical and physical pressure. The dome-like behaviour around EG∼0 combined with our transport, thermodynamic and optical results are fully consistent with an excitonic insulator phase in Ta2NiSe5.
Lu , Y F , Kono , H , Larkin , T I , Rost , A W , Takayama , T , Boris , A V , Keimer , B & Takagi , H 2017 , ' Zero-gap semiconductor to excitonic insulator transition in Ta 2 NiSe 5 ' , Nature Communications , vol. 8 , 14408 . https://doi.org/10.1038/ncomms14408
© The Author(s) 2017. This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
DescriptionThis work was partially supported by Grant-in-Aid for Scientific Research (S; grant no. 24224010) and by Grant-in-Aid for Scientific Research on Innovative Areas (grant no. JP15H05852). H.T. acknowledges support from the Alexander von Humboldt foundation.
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.