  In this work we investigate quantum transport in Cu nanowires created by
bringing macroscopic Cu wires into and out of contact under an applied magnetic
field in air. Here we show that a 70 % magneto-conductance effect can be seen
in a Cu nanowire in a field of 2 mT at room temperature. We propose that this
phenomenon is a consequence of spin filtering due to the adsorption of
atmospheric oxygen modifying the electronic band structure and introducing spin
split conduction channels. This is a remarkable result since bulk Cu is not
magnetic and it may provide a new perspective in the quest for spintronic
devices.
