Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electron-hole symmetry in a semiconducting carbon nanotube quantum dot   Optical and electronic phenomena in solids arise from the behaviour of
electrons and holes (unoccupied states in a filled electron sea). Electron-hole
symmetry can often be invoked as a simplifying description, which states that
electrons with energy above the Fermi sea behave the same as holes below the
Fermi energy. In semiconductors, however, electron-hole symmetry is generally
absent since the energy band structure of the conduction band differs from the
valence band. Here we report on measurements of the discrete, quantized-energy
spectrum of electrons and holes in a semiconducting carbon nanotube. Through a
gate, an individual nanotube is filled controllably with a precise number of
either electrons or holes, starting from one. The discrete excitation spectrum
for a nanotube with N holes is strikingly similar to the corresponding spectrum
for N electrons. This observation of near perfect electron-hole symmetry
demonstrates for the first time that a semiconducting nanotube can be free of
charged impurities, even in the limit of few-electrons or holes. We furthermore
find an anomalously small Zeeman spin splitting and an excitation spectrum
indicating strong electron-electron interactions.

17
The categories of this paper are: q-fin
15
The categories of this paper are: nucl-ex
18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat