We report the realization of novel symmetry-protected Dirac fermions in a surface-doped two-dimensional (2D) semiconductor, black phosphorus. The widely tunable band gap of black phosphorus by the surface Stark effect is employed to achieve a surprisingly large band inversion up to ∼0.6 eV. High-resolution angle-resolved photoemission spectra directly reveal the pair creation of Dirac points and their movement along the axis of the glide-mirror symmetry. Unlike graphene, the Dirac point of black phosphorus is stable, as protected by space-time inversion symmetry, even in the presence of spin-orbit coupling. Our results establish black phosphorus in the inverted regime as a simple model system of 2D symmetry-protected (topological) Dirac semimetals, offering an unprecedented opportunity for the discovery of 2D Weyl semimetals.
Bibliographical noteFunding Information:
This work was supported by the National Research Foundation (NRF) of Korea (Grants No. 2017R1A2B3011368, No. 2017R1A5A1014862), and Institute for Basic Science (Grant No. IBS-R014-D1), New Faculty Research Seed Funding Grant and Future-leading Research Initiative of 2017-22-0059 funded by Yonsei University, and the POSCO Science Fellowship of POSCO TJ Park Foundation. S. S. B and H. J. C. acknowledge support from the NRF (Grant No. 2011-0018306). Computational resources have been provided by Korea Institute of Science and Technology Information Supercomputing Center (Projects No. KSC-2016-C3-0006 and No. KSC-2017-C3-0020). B.-J. Y. was supported by Institute for Basic Science (Grant No. IBS-R009-D1), Research Resettlement Fund for the new faculty of Seoul National University, and Basic Science Research Program through the NRF of Korea (Grant No. 0426-20150011). J. K. was supported by NRF Grant (NRF-2016-Fostering Core Leaders of the Future Basic Science Program/Global Ph.D. Fellowship Program). We thank W. J. Shin, J. Denlinger, Y. K. Kim, A. Bostwick, and E. Rotenberg for help in ARPES experiments, and H. W. Yeom for financial support at the early stage of this work.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)