Tuning of Topological Dirac States via Modification of van der Waals Gap in Strained Ultrathin Bi₂Se₃ Films

Abstract

Robust massless Dirac states with helical spin textures were realized at the boundaries of topological insulators such as van der Waals (vdW) layered Bi2Se3 family compounds. Topological properties of massless Dirac states can be controlled by varying the film thickness, external stimuli, or environmental factors. Here, we report single-crystal-quality growth of ultrathin Bi2Se3 films on flexible polyimide sheets and manipulation of the Dirac states by varying the vdW gap. X-ray diffraction unambiguously demonstrates that under uniaxial bending stress the vdW gap substantially changes with interatomic-layer distances unaltered. Terahertz and photoelectron spectroscopy indicate tuning of the number of quantum conducting channels and of work function, by the stress, respectively. Surprisingly, under compressive strain, transport measurements reveal dimensional crossover and suppressed weak antilocalization. First-principles calculations support the observation. Our findings suggest that variation of vdW gap is an effective means of tuning the Fermi level and topological Dirac states for spintronics and quantum computation.

Unraveling the dislocation core structure at a van der Waals gap in bismuth telluride

“…Such strain fields are characterized by alternating tension and compression regions. Experiments and first-principles calculations [15,20] have shown that application of tensile and compressive strains across the van der Waals gap in Bi 2 Se 3 strongly affects the electronic band structure. Tensile strain was found to shift the Dirac point while com-pressive strain opened a gap and destroyed the Dirac states.…”

Ultrafast Carrier–Lattice Interactions and Interlayer Modulations of Bi2Se3 by X-ray Free-Electron Laser Diffraction

“…34 , we calculated the band structures for different interlayer distances (𝑠 + 𝑠) while keeping the atomic structure within the QL fixed. The band structure near the  point and corresponding projected density of states (PDOS) with interlayer distance changes (𝑠 in inset) are overlaid in Figure4c.…”

“…To investigate how interlayer distance modulation affects the topological phase of Bi 2 Se 3 , , we calculated the band structures for different interlayer distances ( s + Δ s ) while keeping the atomic structure within the QL fixed. The calculation is carried out for the ground state without considering the carriers since most carriers are relaxed 20 ps after the laser excitation.…”

Proximity effect in a superconductor–topological insulator heterostructure based on first principles

“…As required in the SKKR formalism, the SC-TI heterostructures are divided into three regions, I-III [ Fig. 1 is made to avoid an effect of strain on the topological surface states [33,34]. The out-of-plane lattice constant for PdTe is slightly expanded to conserve the volume of PdTe.…”