Strain-induced Dirac state shift in topological insulator Bi2Se3 nanowires

Abstract

In this study, we demonstrate the possibility to tune Dirac surface states of a three-dimensional topological insulator (TI) by applying external strain to single-crystalline Bi2Se3 nanowires (NWs). The NWs were placed over 200 nm deep trenches, which leads to a significant bending, resulting in tensile strain at the bottom surface of the wire and compressive strain at its top surface. By performing low-temperature magnetotransport measurements, we were able to show that TI surfaces under compressive or tensile strain (ϵ=±0.1%) experience a significant Dirac shift of ΔE=∓30 meV as compared to relaxed surfaces. For surface states under tensile strain, an increased carrier mobility is indicated. The opportunity to externally tune the Dirac states therefore could lead to further improvement in future TI devices.

Strain-driven tunable topological states in Bi2Se3

“…Experiments show that alternating edge dislocation pairs along the boundary introduce periodic in-plane tensile and compressive strains, which in turn shift the energy of the Dirac state and open a gap [28]. Also, straininduced reversible Fermi level tuning in Sb 2 Te 3 films [29] and Dirac state shifts in single-crystal Bi 2 Se 3 nanowires bent by an external force have been reported [30]. Furthermore, recent studies point to the feasibility to induce controllable strain either in thin films or 2D structures.…”

Realization of a New Topological Crystalline Insulator and Lifshitz Transition in PbTe

“…Our magneto‐transport experiments on nonstoichiometric epitaxial PbTe(111) films confirm that a new topological phase is realized by introducing Te Pb into PbTe. Since it has been reported that strain can tune Dirac states and induce topological phase transition in TIs, the new topological phase is further explored with transport measurements under external pressure. The experimental results show a nonmonotonic change of the Fermi surface (FS), carrier density, and effective mass with increasing pressure, which can be ascribed to a pressure induced Lifshitz transition based on our theoretical calculations.…”

Tuning topology in thin films of topological insulators by strain gradients

“…Using that v A 2 4 eVÅ, we find that thin films of 2.6 nm thickness can be driven via the topological phase transition for a strain-gradient induced coupling of V 55 meV. By considering that strain-induced shift of Dirac cones of V 30 meV have been achieved with a maximal strain at the top (bottom) surface of ±0.1% [29], one can therefore expect that the strain-gradient induced topological phase transition would require a maximal strain 1%, or equivalently a bending radius of 260 nm. The tunability of the topology in 3DTI thin films by means of inhomogeneous strains is similar in nature to the one achievable by means of externally applied electric fields, since they also provide a source of structure inversion asymmetry.…”

“…Let us consider for instance the strain pattern due to a mechanical bending of the thin film. Such a mechanical deformation has been very recently achieved by placing single-crystalline Bi 2 Se 3 nanowires over deep trenches [29]. It can be also realized by external force loading using an atomic force microscope as recently employed to induce large flexoelectric effects in strontium titanate single crystals [30].…”