Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An ultra-broadband electromagnetically indefinite medium formed by
  aligned carbon nanotubes   Anisotropic materials with different signs of components of the permittivity
tensor are called indefinite materials. Known realizations of indefinite media
suffer of high absorption losses. We show that periodic arrays of parallel
carbon nanotubes (CNTs) can behave as a low-loss indefinite medium in the
infrared range. We show that a finite-thickness slab of CNTs supports the
propagation of backward waves with small attenuation in an ultra-broad
frequency band. In prospective, CNT arrays can be used for subwavelength
focusing and detection, enhancing the radiation efficiency of small sources.

29
The categories of this paper are: funct-an
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
13
The categories of this paper are: quant-ph