Magnetoresistance in underdoped YBa2Cu3O6+x: implications for unusual normal state

The striking properties of high-Tc cuprates are likely caused by the interplay of their electron and magnetic subsystems, which makes the magnetic field to be a special tool in elucidating their nature. We have measured the in-plane and out-of-plane magnetoresistance (MR) on heavily underdoped YBa2Cu3O6+x. The c-axis MR demonstrates a sharp increase at the Neel temperature while the in-plane MR is small and smooth through TN, which points to the essential role of the spin fluctuations only in the interplane transport. We have found also a low-field negative MR emerging for both the in-plane and c-axis transport in antiferromagnetic YBa2Cu3O6+x. The latter feature can be well understood only assuming doped holes to be segregated into stripes at these heavily underdoped compositions. (author)