Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Response of an electron system to a periodic potential   We give a quantum field theoretical treatment of a one dimensional electron
system with a fixed chemical potential $\mu$. The non-perturbative Lindhard
response function is found for an electron system in a sinusoidal potential.

15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
2
The categories of this paper are: math
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat