Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Robust Gapless Surface State against Surface Magnetic Impurities on
  (Bi$_{0.5}$Sb$_{0.5}$)$_2$Te$_3$ Evidenced by In Situ Magnetotransport
  Measurements   Despite extensive experimental and theoretical efforts, the important issue
of the effects of surface magnetic impurities on the topological surface state
of a topological insulator (TI) remains unresolved. We elucidate the effects of
Cr impurities on epitaxial thin films of (Bi$_{0.5}$Sb$_{0.5}$)$_{2}$Te$_{3}$:
Cr adatoms are incrementally deposited onto the TI held in ultrahigh vacuum at
low temperatures, and \textit{in situ} magnetoconductivity and Hall effect
measurements are performed at each increment with electrostatic gating. In the
experimentally identified surface transport regime, the measured minimum
electron density shows a non-monotonic evolution with the Cr density
($n_{\mathrm{Cr}}$): it first increases and then decreases with
$n_{\mathrm{Cr}}$. This unusual behavior is ascribed to the dual roles of the
Cr as ionized impurities and electron donors, having competing effects of
enhancing and decreasing the electronic inhomogeneities in the surface state at
low and high $n_{\mathrm{Cr}}$ respectively. The magnetoconductivity is
obtained for different $n_{\mathrm{Cr}}$ on one and the same sample, which
yields clear evidence that the weak antilocalization effect persists and the
surface state remains gapless up to the highest $n_{\mathrm{Cr}}$, contrary to
the expectation that the deposited Cr should break the time reversal symmetry
and induce a gap opening at the Dirac point.

35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
6
The categories of this paper are: astro-ph
7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
11
The categories of this paper are: hep-lat
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
1
The categories of this paper are: cs