New Journal of Physics (Jan 2014)

Strain driven topological phase transitions in atomically thin films of group IV and V elements in the honeycomb structures

  • Zhi-Quan Huang,
  • Chia-Hsiu Hsu,
  • Feng-Chuan Chuang,
  • Yu-Tzu Liu,
  • Hsin Lin,
  • Wan-Sheng Su,
  • Vidvuds Ozolins,
  • Arun Bansil

DOI
https://doi.org/10.1088/1367-2630/16/10/105018
Journal volume & issue
Vol. 16, no. 10
p. 105018

Abstract

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We have investigated topological electronic properties of freestanding bilayers of group IV (C, Si, Ge, Sn, and, Pb) and V (As, Sb, and, Bi) elements of the periodic table in the buckled and planar honeycomb structures under isotropic strain using first-principles calculations. Our focus is on mapping strain driven phase diagrams and identifying topological phase transitions therein as a pathway for guiding search for suitable substrates to grow two-dimensional (2D) topological insulators (TIs) films. Bilayers of group IV elements, excepting Pb, generally transform from trivial metal $\to $ topological metal $\to $ TI $\to $ topological metal $\to $ trivial metal phase with increasing strain from negative (compressive) to positive (tensile) values. Similarly, among the group V elements, As and Sb bilayers transform from trivial metal $\to $ trivial insulator $\to $ TI phase, while Bi transforms from a topological metal to TI phase. The band gap of 0.5 eV in the TI phase of Bi is the largest we found among all bilayers studied, with the band gap increasing further under tensile strain. Differences in the topological characteristics of bilayers of group V elements reflect associated differences in the strength of the spin–orbit coupling (SOC). We show, in particular, that the topological band structure of Sb bilayer becomes similar to that of a Bi bilayer when the strength of the SOC in Sb is artificially enhanced by a factor of 4. This study provides the first report that As can be a 2D TI under tensile strain. Notably, we found the existence of TI phases in all elemental bilayers we studied, except Pb.

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