  Recent analyses of mm-wavelength protoplanetary disk observations have
revealed several emission excesses on the previously identified dust rings,
referred to as dust shoulders. The prevalence of dust shoulders suggests that
they trace a common but unclear mechanism. In this work, we combine 3D,
multifluid hydrodynamic simulations with radiative transfer calculations to
explain the formation of dust shoulders. We find that the ring-shoulder pairs
can result from the 3D planet-disk interactions with massive, gap-opening
planets. The key driver is the dust filtration effect at the local pressure
maximum due to planet-driven outward gas flows. Our work provides a possible
explanation for the outer dust shoulders in recent super-resolution analyses of
ALMA observations. It also provides insights into the formation of the inner
dust shoulder in the PDS 70 disk and highlights the role of 3D effects in
planet-disk interaction studies.
