Tuning a Topological Insulator By Strain

Three-dimensional topological insulators (TIs) are a newly discovered quantum phase of matter distinct from the classic dichotomy of metals and insulators. Although the bulk is nominally insulating, the two-dimensional surface bands form a Dirac cone populated by massless fermions. These surface states are topologically protected against disorder scattering and are spin-polarized. Hence TIs are expected to produce new functionalities for a wide range of applications such as low power electronics (owing to dissipationless transport), spintronics (utilizing spin-polarized current), and quantum information technology.

Here, we show that Dirac states can be tuned by strain at low-angle grain boundaries (GBs) in Bi2Se3(0001), which consist of alternating edge dislocation pairs. Strain fields introduced by these dislocations are found to be in-plane tensile and compressive, leading to periodic depressions and expansions, respectively, in the [0001] direction along the boundary. We further show that Dirac states are enhanced under tensile strain, and destroyed under compressive strain as evident from the opening of a gap in the local density of states. The tuning of Dirac states, demonstrated here near Bi2Se3 GBs, provides the first direct experimental evidence at the atomic scale that Dirac states are tunable by strain, in addition to electric field.

Published in Nature Physics:
“Tuning Dirac states by strain in the topological insulator Bi2Se3“, Y. Liu, Y. Y. Li, S. Rajput, D. Gilks, L. Lari, P. L. Galindo, M. Weinert, V. K. Lazarov, and L. Li, Nature Physics 10, 294-299 (2014).

• Also see News and Views: “Topological insulators: Strain away“, Nature Physics 10, 247-248 (2014).
• Work featured as the cover image of Nature Physics (see image shown above).