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Evidence of high-temperature exciton condensation in a two-dimensional semimetal

Journal Article · · Nature Communications
 [1];  [2];  [3];  [4];  [4];  [3];  [5];  [5];  [6];  [3];  [3];  [7];  [4]
  1. Shanghai Jiao Tong Univ. (China); Shanghai Jiao Tong University, Shanghai (China)
  2. Academia Sinica, Taipei (Taiwan); National Center for Theoretical Sciences, Taipei (Taiwan)
  3. Univ. of Science and Technology of China, Hefei (China)
  4. Shanghai Jiao Tong Univ. (China)
  5. Chinese Academy of Sciences (CAS), Shanghai (China). Shanghai Institute of Microsystem and Information Technology (SIMIT)
  6. Univ. of Science and Technology of China, Hefei (China); Chinese Academy of Sciences (CAS), Shanghai (China). Shanghai Institute of Microsystem and Information Technology (SIMIT)
  7. Univ. of Illinois at Urbana-Champaign, IL (United States)
+ Show Author Affiliations
Electrons and holes can spontaneously form excitons and condense in a semimetal or semiconductor, as predicted decades ago. This type of Bose condensation can happen at much higher temperatures in comparison with dilute atomic gases. Two-dimensional (2D) materials with reduced Coulomb screening around the Fermi level are promising for realizing such a system. Here we report a change in the band structure accompanied by a phase transition at about 180 K in single-layer ZrTe2 based on angle-resolved photoemission spectroscopy (ARPES) measurements. Below the transition temperature, gap opening and development of an ultra-flat band top around the zone center are observed. This gap and the phase transition are rapidly suppressed with extra carrier densities introduced by adding more layers or dopants on the surface. The results suggest the formation of an excitonic insulating ground state in single-layer ZrTe2, and the findings are rationalized by first-principles calculations and a self-consistent mean-field theory. Our study provides evidence for exciton condensation in a 2D semimetal and demonstrates strong dimensionality effects on the formation of intrinsic bound electron–hole pairs in solids.
Research Organization:
Univ. of Illinois at Urbana-Champaign, IL (United States)
Sponsoring Organization:
Ministry of Science and Technology of China; National Natural Science Foundation of China (NSFC); Science and Technology Commission of Shanghai Municipality; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE)
Grant/Contract Number:
FG02-07ER46383
OSTI ID:
2419201
Journal Information:
Nature Communications, Journal Name: Nature Communications Journal Issue: 1 Vol. 14; ISSN 2041-1723
Publisher:
Nature Publishing GroupCopyright Statement
Country of Publication:
United States
Language:
English

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