Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Unexpectedly robust protection from backscattering in the topological
  insulator Bi$_{1.5}$Sb$_{0.5}$Te$_{1.7}$Se$_{1.3}$   Electron scattering in the topological surface state (TSS) of the
bulk-insulating topological insulator Bi$_{1.5}$Sb$_{0.5}$Te$_{1.7}$Se$_{1.3}$
was studied using quasiparticle interference observed by scanning tunneling
microscopy. It was found that not only the 180$^{\circ}$ backscattering but
also a wide range of backscattering angles of 100$^{\circ}$--180$^{\circ}$ is
effectively prohibited in the TSS. This conclusion was obtained by comparing
the observed scattering vectors with the diameters of the constant-energy
contours of the TSS, which were measured for both occupied and unoccupied
states using time- and angle-resolved photoemission spectroscopy. The
unexpectedly robust protection from backscattering in the TSS is a good news
for applications, but it poses a challenge to the theoretical understanding of
the transport in the TSS.

15
The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
31
The categories of this paper are: ao-sci
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys