  Magnon-mediated spin transport across nonmagnetic metal (NM) and
ferromagnetic insulator (FI) interface depends critically on electron-magnon
coupling. We propose a novel route to enhance electron-magnon coupling
dynamically from transport viewpoint. Using non-equilibrium Green's function a
theoretical formalism for magnon-mediated spin current is developed. In the
language of transport, the effective electron-magnon coupling at NM/FI
interface is determined by self-energy of FI lead, which is proportional to
density of states (DOS) at NM/FI interface due to nonlinear process of
electron-magnon conversion. By modifying interfacial DOS, the spin conductance
of 2D and 3D NM/FI systems can be increased by almost three orders of
magnitude, setting up a new platform of manipulating dynamical electron-magnon
coupling.
