Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Phonon-mediated negative differential conductance in molecular quantum
  dots   Transport through a single molecular conductor is considered, showing
negative differential conductance behavior associated with phonon-mediated
electron tunneling processes. This theoretical work is motivated by a recent
experiment by Leroy et al. using a carbon nanotube contacted by an STM tip
[Nature {\bf 432}, 371 (2004)], where negative differential conductance of the
breathing mode phonon side peaks could be observed. A peculiarity of this
system is that the tunneling couplings which inject electrons and those which
collect them on the substrate are highly asymmetrical. A quantum dot model is
used, coupling a single electronic level to a local phonon, forming polaron
levels. A "half-shuttle" mechanism is also introduced. A quantum kinetic
formulation allows to derive rate equations. Assuming asymmetric tunneling
rates, and in the absence of the half-shuttle coupling, negative differential
conductance is obtained for a wide range of parameters. A detailed explanation
of this phenomenon is provided, showing that NDC is maximal for intermediate
electron-phonon coupling. In addition, in absence of a gate, the "floating"
level results in two distinct lengths for the current plateaus, related to the
capacitive couplings at the two junctions. It is shown that the "half-shuttle"
mechanism tends to reinforce the negative differential regions, but it cannot
trigger this behavior on its own.

15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
36
The categories of this paper are: cmp-lg
24
The categories of this paper are: dg-ga
19
The categories of this paper are: eess
2
The categories of this paper are: math
3
The categories of this paper are: physics
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn