Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Topographic Mapping of the Quantum Hall Liquid using a Few-Electron
  Bubble   A scanning probe technique was used to obtain a high-resolution map of the
random electrostatic potential inside the quantum Hall liquid. A sharp metal
tip, scanned above a semiconductor surface, sensed charges in an embedded
two-dimensional electron gas. Under quantum Hall effect conditions, applying a
positive voltage to the tip locally enhanced the 2D electron density and
created a ``bubble'' of electrons in an otherwise unoccupied Landau level. As
the tip scanned along the sample surface, the bubble followed underneath. The
tip sensed the motions of single electrons entering or leaving the bubble in
response to changes in the local 2D electrostatic potential.

2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
32
The categories of this paper are: atom-ph
29
The categories of this paper are: funct-an
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs