Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spontaneous Formation of a Superconductor-Topological Insulator-Normal
  Metal Layered Heterostructure   The discovery of graphene has spurred vigorous investigation of 2D materials,
revealing a wide range of extraordinary properties and functionalities. 2D
heterostructural materials have recently been fabricated by assembling isolated
planes layer-by-layer in a desired sequence. Unusual properties and novel
physical phenomena have been unveiled in such layered heterostructures. For
example, Hofstadter's butterfly, an intriguing pattern of the energy states of
Bloch electrons, was predicted several decades ago to be observable only under
unfeasibly strong magnetic fields in conventional materials. But it has been
observed recently under current experimental conditions in graphene/BN layered
heterostructures, one of the outstanding new kinds of 2D materials. Moreover,
another amazing physics phenomenon, Majorana fermions was predicted to exist in
heterostructural systems consisting of a superconductor (SC) and a topological
insulator (TI) Journal.

31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
6
The categories of this paper are: astro-ph
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
1
The categories of this paper are: cs
35
The categories of this paper are: mtrl-th
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
23
The categories of this paper are: solv-int