Tuning the Fermi level with topological phase transition by internal strain in a topological insulator Bi₂Se₃thin film

Abstract

In a three-dimensional topological insulator Bi2Se3, a stress control for band gap manipulation was predicted but no systematic investigation has been performed yet due to the requirement of large external stress. We report herein on the strain-dependent results for Bi2Se3 films of various thicknesses that are grown via a self-organized ordering process. Using small angle X-ray scattering and Raman spectroscopy, the changes of d-spacings in the crystal structure and phonon vibration shifts resulted from stress are clearly observed when the film thickness is below ten quintuple layers. From the UV photoemission/inverse photoemission spectroscopy (UPS/IPES) results and ab initio calculations, significant changes of the Fermi level and band gap were observed. The deformed band structure also exhibits a Van Hove singularity at specific energies in the UV absorption experiment and ab initio calculations. Our results, including the synthesis of a strained ultrathin topological insulator, suggest a new direction for electronic and spintronic applications for the future.

Strain-driven tunable topological states in Bi2Se3

“…In the last few years, topology has been found to play an essential role in defining many phases of matter such as the quantum Hall effect [1], the quantum spin-Hall effect [6,7], the quantum anomalous Hall effect [8,9], Weyl semimetals [10][11][12] or topological nodal line semimetals [13][14][15] to mention just a few. Specifically, Bi-chalcogenide three-dimensional TIs are characterized by a non-zero 2  topological invariant, and according to the bulk-to-boundary correspondence [5,16], they exhibit topological states at the boundary with any material with a different value of the topological invariant. In particular, Bi-chalcogenide TIs host gapless surface states that are topologically protected by time-reversal symmetry.…”

“…Furthermore, recent studies point to the feasibility to induce controllable strain either in thin films or 2D structures. Strained structures of a single material such as Bi 2 Se 3 films [16], layered structures containing two compounds such as Bi 2 Te 3 /Sb 2 Te 3 [31] and Bi 2 Se 3 /In 2 Se [22] or even Bi 2 Se 3 /Bi 2 Te 3 lateral heterojunctions with a large lattice mismatch [32] have been synthesized. In these strained structures either uniform strain or a strain gradient is achieved.…”

Strain effects in topological insulators: Topological order and the emergence of switchable topological interface states in Sb2Te3/Bi2Te3Aramberri1, Muñoz2 2017Phys. Rev. B455421View full textAdd to dashboardCite

“…This technique has already been experimentally demonstrated and developed by Koski et al 15 in Bi 2 Se 3 to effectively enhance the c lattice parameter without disrupting the ionic or electronic configuration. In addition, Bi 2 Se 3 films under tensile stress along the c-axis have been recently grown via a self-organized order method and significant changes of the Fermi level and band gap of those films have been measured 16 . Topological state shifts at the strained grain boundaries in Bi 2 Se 3 films have also been reported 8 .…”

Closing the Surface Bandgap in Thin Bi2Se3/Graphene Heterostructures

“…This confirms our previous results for Bi 2 Se 3 film on a SiO 2 substrate without graphene. 24 In case of a SiO 2 substrate without graphene, there is a dramatic increase in the d-spacing value, from 9.542 Å for 30 QL Bi 2 Se 3 to 10.478 Å for 2 QL Bi 2 Se 3 , which results from the typical growth process using a self-ordering growth mechanism during the post annealing process. The strain values of thicker films on the graphene substrates with thicknesses greater than 5 QL are similar to those on SiO 2 substrates.…”