Gigantic Nonreciprocal Conduction at a Polar-Magnetic Interface of GdTiO_{3}/EuTiO_{3}

Oxide heterostructures provide excellent playgrounds to investigate novel transport phenomena emerging at interfaces due to broken inversion symmetry, in stark contrast to constituent compounds. Here, we fabricate GdTiO_{3}/EuTiO_{3} heterostructures, where a two-dimensional electron system emerges due to the Ti^{3+}/Ti^{4+} valence-mismatch interface in the background of a large magnetic moment from half-filled 4f electrons on Gd^{3+} and Eu^{2+} ions. Reflecting the coexistence of electric polarization and magnetism at the interface, nonreciprocal transport properties are observed, with distinct dependencies on temperature and magnetic field, originating from the scattering by chiral magnons. We discovered that, despite the extremely small Rashba band splitting, the nonreciprocal conduction is surprisingly large, presenting a promising route to the materials design of polar-magnetic metals composed of transition metal oxides.