  Coupling of an atom-like emitter to surface plasmons provides a path toward
significant optical nonlinearity, which is essential in quantum information
processing and quantum networks. A large coupling strength requires
nanometer-scale positioning accuracy of the emitter near the surface of the
plasmonic structure, which is challenging. We demonstrate the coupling of
single localized defects in a tungsten diselenide (WSe2) monolayer self-aligned
to the surface plasmon mode of a silver nanowire. The silver nanowire induces a
strain gradient on the monolayer at the overlapping area, leading to the
formation of localized defect emission sites that are intrinsically close to
the surface plasmon. We measure a coupling efficiency with a lower bound of 39%
from the emitter into the plasmonic mode of the silver nanowire. This technique
offers a way to achieve efficient coupling between plasmonic structures and
localized defects of 2D semiconductors.
