  In this paper we consider a new mechanism for stopping the inward migration
of a low-mass planet embedded in a gaseous protoplanetary disc. It operates
when a low-mass planet (for example a super-Earth), encounters outgoing density
waves excited by another source in the disc. This source could be a gas giant
in an orbit interior to that of the low-mass planet. As the super-Earth passes
through the wave field, angular momentum is transferred to the disc material
and then communicated to the planet through coorbital dynamics, with the
consequence that its inward migration can be halted or even reversed. We
illustrate how the mechanism we consider works in a variety of different
physical conditions employing global two-dimensional hydrodynamical
calculations. We confirm our results by performing local shearing box
simulations in which the super-Earth interacts with density waves excited by an
independent harmonically varying potential. Finally, we discuss the constraints
arising from the process considered here, on formation scenarios for systems
containing a giant planet and lower mass planet in an outer orbit with a 2:1
commensurability such as GJ876.
