  Rhombohedral graphene multilayers host various broken-symmetry metallic
phases as well as superconductors whose pairing mechanism and order parameter
symmetry remain unsettled. Strikingly, experiments have revealed prominent new
superconducting regions in rhombohedral bilayer and trilayer graphene devices
with proximity-induced Ising spin-orbit coupling. We propose that these
superconductors descend from a common spin-canted normal state that
spontaneously breaks a U(1) spin symmetry and thus supports a gapless
(Goldstone) magnon mode. In particular, we develop a scenario wherein pairing
in the spin-canted state emerges from a novel type of magnon-mediated
attraction: Contrary to conventional mechanisms that involve the exchange of a
single boson, we show that second-order processes that exchange two magnons are
dominant and produce an $s$-wave pairing interaction featuring a unique
logarithmic low-frequency divergence. This low-frequency divergence disappears
when spin-orbit coupling vanishes, providing a promising explanation for
spin-orbit-enabled pairing. Numerous other experimental observations --
including nontrivial dependence of superconductivity on the spin-orbit coupling
strength, in-plane magnetic fields, and Fermi surface structure -- also
naturally follow from our scenario.
