Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Non-magnetic negative-refraction systems for terahertz and far-infrared
  frequencies   We demonstrate that homogeneous naturally-occurring materials can form
non-magnetic negative refractive index systems, and present specific
realizations of the proposed approach for the THz and far-IR frequencies. The
proposed structure operates away from resonance, thereby promising the capacity
for low-loss devices.

21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs