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Title: Charge density wave transition in single-layer titanium diselenide

A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene--a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering. The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The behavior of the Bardeen-Cooper-Schrieffer (BCS) gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [6] ;  [6] ;  [7]
  1. Univ. of Illinois, Urbana-Champaign, IL (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Academia Sinica, Taipei (Taiwan)
  3. Univ. of Illinois, Urbana-Champaign, IL (United States)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Nanjing Univ. (China); SLAC National Accelerator Lab., Menlo Park, CA (United States)
  5. Academia Sinica, Taipei (Taiwan); Georgia Inst. of Technology, Atlanta, GA (United States); National Taiwan Univ., Taipei (Taiwan)
  6. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  7. Univ. of Illinois, Urbana-Champaign, IL (United States); National Taiwan Univ., Taipei (Taiwan)
Publication Date:
OSTI Identifier:
1237589
Grant/Contract Number:
AC03-76SF00515
Type:
Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 6; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Research Org:
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE physical sciences; condensed matter