Nonreciprocal spin current generation in surface-oxidized copper films

Okano, Genki*; Matsuo, Mamoru; Onuma, Yuichi*; Maekawa, Sadamichi*; Nozaki, Yukio*

We experimentally demonstrate the nonreciprocal generation of spin current () in a surface-oxidized copper film. The efficiency of conversion is at least 320 times larger than the inverse conversion. This nonreciprocity is due to a novel type of generation, which relies on the transfer of angular momentum from the velocity field of free electrons. A gradient in the electrical mobility in the film produces vorticity in the in-plane drift velocity of the free electrons. The inverse process can hardly occur when is collinear with the gradient in the electrical mobility.