Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical probe of electrostatic doping in an n-type Mott insulator   Electrostatic doping into an $n$-type Mott insulator Sm$_{2}$CuO$_{4}$ has
been successfully achieved with use of the heterojunction with an
  $n$-type band semiconductor Nb-doped SrTiO$_{3}$. The junction exhibits
rectifying current-voltage characteristics due to the interface band
discontinuity and the formation of depleted region. The application of reverse
bias electric field on this junction enables the field-effect electron doping
(presumably up to 6% per Cu atom) to the Mott insulator. The electro-modulation
absorption spectroscopy could clearly show a large modification of the Mott-gap
state accompanying the spectral weight transfer to the lower-energy region,
reminiscent of formation of a metallic state.

34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
7
The categories of this paper are: hep-th
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con