Positron surface state as a spectroscopic probe for characterizing surfaces of topological insulator materials

Abstract

Topological insulators are attracting considerable interest due to their potential for technological applications and as platforms for exploring wide-ranging fundamental science questions. In order to exploit, fine-tune, control and manipulate the topological surface states, spectroscopic tools which can effectively probe their properties are of key importance. Here, we demonstrate that positrons provide a sensitive probe for topological states, and that the associated annihilation spectrum provides a new technique for characterizing these states. Firm experimental evidence for the existence of a positron surface state near Bi2Te2Se with a binding energy of E b = 2.7 ± 0.2 eV is presented, and is confirmed by first-principles calculations. Additionally, the simulations predict a significant signal originating from annihilation with the topological surface states and shows the feasibility to detect their spin-texture through the use of spin-polarized positron beams.

Experimental and computational studies of positron-stimulated ion desorption from TiO2(1 1 0) surface

“…The local density approximation functional [20] was used for the positron-electron correlation energy and potential. The corrugated mirror model [21][22][23] (CMM) was adopted to represent the positron surface potential precisely. In the CMM, asymptotic behaviour of the image potential, V im (z), is adapted to the positron-electron correlation potential in the vacuum region.…”

Application of the weighted-density approximation to the accurate description of electron-positron correlation effects in materials

“…The corrugated mirror model suffers from a number of flaws even though its results agree reasonably with experiments 13,[22][23][24][25] . In particular, while it is straightforward to construct the corrugated image potential for perfect surfaces, this quickly becomes unfeasible for more complex surfaces.…”

“…For the calculation of positron lifetimes, the local density n e in the enhancement factor has to be replaced by the effective density n * e , λ a = 1 τ = πr 2 e c dr n e (r)n p (r)γ(n * e (r)). (19) We note that the pair correlation function in this approach does not satisfy the Kimball cusp condition (13), and as discussed earlier, there is no formal reason why the sum rule should hold. We will return to investigate the effect of modifying the sum rule below.…”

Observation of a charge delocalization from Se vacancies inBi2Se3: A positron annihilation study of native defects

“…Although the origin of this component is not entirely clear, it is supposed to be related with the positronium formation on the surface. Indeed, recent works demonstrate the existence of positron surface states on topological insulators [56]. The second lifetime component is related with the positron annihilation in Kapton, which is 382 ps [57,58].…”