Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum cascade phenomenon in natural atomic superlattices formed in
  Bi2Sr2CaCu2O8 single crystals   Natural atomic superlattices are formed in certain strongly anisotropic
layered compound. Here we study interlayer transport in single crystals of
Bi2Sr2CaCu2O8 cuprates, which represent stacks of atomic scale intrinsic
Josephson junctions. A series of resonant dips in conductance is observed at
condition when bremsstrahlung and recombination bands in non-equilibrium
spectrum of Josephson junctions overlap. The phenomenon is explained in terms
of self-detection of a new type of collective strongly non-equilibrium state in
stacked Josephson junctions, bearing certain resemblance with operation of a
Quantum Cascade Laser. Conclusions are supported by in-situ
generation-detection experiments, providing evidence for cascade amplification
of recombination radiation, and by numerical simulations.

5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
10
The categories of this paper are: q-bio
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
36
The categories of this paper are: cmp-lg
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph