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Title: Dirac mass generation from crystal symmetry breaking on the surfaces of topological crystalline insulators

Abstract

The tunability of topological surface states and controllable opening of the Dirac gap are of fundamental and practical interest in the field of topological materials. In the newly discovered topological crystalline insulators (TCIs), theory predicts that the Dirac node is protected by a crystalline symmetry and that the surface state electrons can acquire a mass if this symmetry is broken. Recent studies have detected signatures of a spontaneously generated Dirac gap in TCIs; however, the mechanism of mass formation remains elusive. In this work, we present scanning tunnelling microscopy (STM) measurements of the TCI Pb 1-xSn xSe for a wide range of alloy compositions spanning the topological and non-topological regimes. The STM topographies reveal a symmetry-breaking distortion on the surface, which imparts mass to the otherwise massless Dirac electrons—a mechanism analogous to the long sought-after Higgs mechanism in particle physics. Interestingly, the measured Dirac gap decreases on approaching the trivial phase, whereas the magnitude of the distortion remains nearly constant. Our data and calculations reveal that the penetration depth of Dirac surface states controls the magnitude of the Dirac mass. At the limit of the critical composition, the penetration depth is predicted to go to infinity, resulting in zero mass,more » consistent with our measurements. Lastly, we discover the existence of surface states in the non-topological regime, which have the characteristics of gapped, double-branched Dirac fermions and could be exploited in realizing superconductivity in these materials.« less

Authors:
 [1];  [2];  [3];  [4];  [1];  [1];  [5];  [6];  [7];  [8];  [9];  [6];  [7];  [5];  [10]
  1. Boston College, Chestnut Hill, MA (United States)
  2. Boston College, Chestnut Hill, MA (United States); Tohoku Univ., Sendai (Japan)
  3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of California, Berkeley, CA (United States)
  4. National Taiwan Univ., Taipei (Taiwan); Academia Sinica, Taipei (Taiwan)
  5. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  6. National Univ. of Singapore (Singapore)
  7. Northeastern Univ., Boston, MA (United States)
  8. Princeton Univ., Princeton, NJ (United States)
  9. National Taiwan Univ., Taipei (Taiwan)
  10. Boston College, Chestnut Hill, MA (United States); Univ. of Illinois Urbana-Champaign, Urbana, IL (United States)
Publication Date:
Research Org.:
Boston College, Chestnut Hill, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1349051
Grant/Contract Number:  
SC0008615
Resource Type:
Accepted Manuscript
Journal Name:
Nature Materials
Additional Journal Information:
Journal Volume: 14; Journal Issue: 3; Journal ID: ISSN 1476-1122
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; topological insulators

Citation Formats

Zeljkovic, Ilija, Okada, Yoshinori, Serbyn, Maksym, Sankar, R., Walkup, Daniel, Zhou, Wenwen, Liu, Junwei, Chang, Guoqing, Wang, Yung Jui, Hasan, M. Zahid, Chou, Fangcheng, Lin, Hsin, Bansil, Arun, Fu, Liang, and Madhavan, Vidya. Dirac mass generation from crystal symmetry breaking on the surfaces of topological crystalline insulators. United States: N. p., 2015. Web. doi:10.1038/nmat4215.
Zeljkovic, Ilija, Okada, Yoshinori, Serbyn, Maksym, Sankar, R., Walkup, Daniel, Zhou, Wenwen, Liu, Junwei, Chang, Guoqing, Wang, Yung Jui, Hasan, M. Zahid, Chou, Fangcheng, Lin, Hsin, Bansil, Arun, Fu, Liang, & Madhavan, Vidya. Dirac mass generation from crystal symmetry breaking on the surfaces of topological crystalline insulators. United States. doi:10.1038/nmat4215.
Zeljkovic, Ilija, Okada, Yoshinori, Serbyn, Maksym, Sankar, R., Walkup, Daniel, Zhou, Wenwen, Liu, Junwei, Chang, Guoqing, Wang, Yung Jui, Hasan, M. Zahid, Chou, Fangcheng, Lin, Hsin, Bansil, Arun, Fu, Liang, and Madhavan, Vidya. Mon . "Dirac mass generation from crystal symmetry breaking on the surfaces of topological crystalline insulators". United States. doi:10.1038/nmat4215. https://www.osti.gov/servlets/purl/1349051.
@article{osti_1349051,
title = {Dirac mass generation from crystal symmetry breaking on the surfaces of topological crystalline insulators},
author = {Zeljkovic, Ilija and Okada, Yoshinori and Serbyn, Maksym and Sankar, R. and Walkup, Daniel and Zhou, Wenwen and Liu, Junwei and Chang, Guoqing and Wang, Yung Jui and Hasan, M. Zahid and Chou, Fangcheng and Lin, Hsin and Bansil, Arun and Fu, Liang and Madhavan, Vidya},
abstractNote = {The tunability of topological surface states and controllable opening of the Dirac gap are of fundamental and practical interest in the field of topological materials. In the newly discovered topological crystalline insulators (TCIs), theory predicts that the Dirac node is protected by a crystalline symmetry and that the surface state electrons can acquire a mass if this symmetry is broken. Recent studies have detected signatures of a spontaneously generated Dirac gap in TCIs; however, the mechanism of mass formation remains elusive. In this work, we present scanning tunnelling microscopy (STM) measurements of the TCI Pb1-xSnxSe for a wide range of alloy compositions spanning the topological and non-topological regimes. The STM topographies reveal a symmetry-breaking distortion on the surface, which imparts mass to the otherwise massless Dirac electrons—a mechanism analogous to the long sought-after Higgs mechanism in particle physics. Interestingly, the measured Dirac gap decreases on approaching the trivial phase, whereas the magnitude of the distortion remains nearly constant. Our data and calculations reveal that the penetration depth of Dirac surface states controls the magnitude of the Dirac mass. At the limit of the critical composition, the penetration depth is predicted to go to infinity, resulting in zero mass, consistent with our measurements. Lastly, we discover the existence of surface states in the non-topological regime, which have the characteristics of gapped, double-branched Dirac fermions and could be exploited in realizing superconductivity in these materials.},
doi = {10.1038/nmat4215},
journal = {Nature Materials},
number = 3,
volume = 14,
place = {United States},
year = {2015},
month = {2}
}

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