Abstract
The protected surface states of topological insulators (TIs) form gapless Dirac cones corresponding non-degenerate eigenstates with helical spin polarisation. The presence of a warping term deforms the isotropic cone of the most simple model into snowflake Fermi surfaces as in Bi2Se3 and Bi2Te3. Their features have been identified in STM quasiparticle interference (QPI) experiments on isolated surfaces. Here we investigate the QPI spectrum for the TI thin-film geometry with finite tunnelling between the surface states. This leads to a dramatic change of spectrum due to gapping and a change in spin texture that should leave distinct signatures in the QPI pattern. We consider both normal and magnetic exchange scattering from the surface impurities and obtain the scattering t-matrix in Born approximation as well as the general closed solution. We show the expected systematic variation of QPI snowflake intensity features by varying film thickness and study, in particular, the influence on backscattering processes. We predict the variation of the QPI spectrum for Bi2Se3 thin films using the observed gap dependence from ARPES results.
Highlights
The most dramatic manifestation in a topological insulator (TI) is the presence of protected surface states which are helical spin locked nondegenerate eigenstates with a gapless Dirac dispersion
We discuss the numerical results for the quasiparticle interference (QPI) spectrum under systematic variation of bias voltage ω = eV, intersurface tunneling t of the thin film and normal (Vc) and magnetic (Vm) impurity scattering potential
The shape of the pattern and its increasing radius with ω is clearly seen in the first row representing the isolated surfaces (t = 0)
Summary
The most dramatic manifestation in a topological insulator (TI) is the presence of protected surface states which are helical spin locked nondegenerate eigenstates with a gapless Dirac dispersion. The tunneling mixes the surfaces states leading to a finite gap at the Dirac point and it lifts their protection as witnessed by the suppression of helical polarization and modification of the Berry phase for states close to the gap energy [18] This has been directly observed in magnetotransport experiments in Bi2Se3 where the weak. Our theoretical approach to them is entirely analytical t-matrix theory [21,22] because we want to study in detail the combined effect of in-plane warping and intersurface hybridization on QPI images This allows a transparent interpretation of their spin texture, Berry phase, and gradual change of backscattering characteristics with intersurface tunneling which are at the heart of the TI thin film problem.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
