Large unidirectional magnetoresistance from the dual functionality of copper oxide in naturally oxidized light-metal Al/Cu bilayer films

Unidirectional magnetoresistance (UMR) has garnered extensive attention for its rich physics and potential applications. The prevailing belief is that indispensable ferromagnetic films serve as scattering sources of polarized electrons or that noncentrosymmetric systems cause spin band splitting, driving most research toward ferromagnet/normal-metal bilayer films or nonmagnetic Rashba systems. However, our observations reveal a significant UMR in bilayer films consisting solely of the oxidized light metal Al/Cu. Remarkably, the UMR signal of 0.073% is approximately one order of magnitude larger than that of most structures. Such a UMR is attributed to the dual functionality of copper oxide, which not only generates polarized electrons---a recognized function---but also scatters these electrons in a weak magnetization manner. Our findings provide a fresh strategy to generate the UMR, facilitating its application through the use of more readily available materials.