Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electrically controlled emission from singlet and triplet exciton
  species in atomically thin light emitting diodes   Excitons are composite bosons that can feature spin singlet and triplet
states. In usual semiconductors, without an additional spin-flip mechanism,
triplet excitons are extremely inefficient optical emitters. Transition metal
dichalcogenides (TMDs), with their large spin-orbit coupling, have been of
special interest for valleytronic applications for their coupling of circularly
polarized light to excitons with selective valley and spin$^{1-4}$. In
atomically thin MoSe$_2$/WSe$_2$ TMD van der Waals (vdW) heterostructures, the
unique atomic registry of vdW layers provides a quasi-angular momentum to
interlayer excitons$^{5,6}$, enabling emission from otherwise dark spin triplet
excitons. Here, we report electrically tunable spin singlet and triplet exciton
emission from atomically aligned TMD heterostructures. We confirm the spin
configurations of the light-emitting excitons employing magnetic fields to
measure effective exciton g-factors. The interlayer tunneling current across
the TMD vdW heterostructure enables the electrical generation of singlet and
triplet exciton emission in this atomically thin PN junction. We demonstrate
electrically tunability between the singlet and triplet excitons that are
generated by charge injection. Atomically thin TMD heterostructure light
emitting diodes thus enables a route for optoelectronic devices that can
configure spin and valley quantum states independently by controlling the
atomic stacking registry.

7
The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
28
The categories of this paper are: alg-geom
19
The categories of this paper are: eess
31
The categories of this paper are: ao-sci
5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin