The Critical Role of the Cuo Chains in Metallizing the C-axis in YBa2Cu3O7−δ

We report measurements of the normal state c-axis magnetoresistance (MR) of untwinned single crystals of slightly overdoped YBa2Cu3O7−δ. An orbital contribution to the transverse MR, a signature of coherent c- axis motion, arises only from the component of the magnetic field perpendicular to the CuO chains. This result implies that the CuO chains are primarily responsible for coherent transport along the c-axis in YBa2Cu3O7−δand that those regions of the CuO2planes that do not involve the chains remain two-dimensional, even in the absence of a normal state gap.