Uniaxial linear resistivity of superconducting La _1.905Ba _0.095CuO ₄ induced by an external magnetic field

We present an experimental study of the anisotropic resistivity of superconducting La _2-xBa _xCuO ₄ with x=0.095 and transition temperature T _c=32 K. In a magnetic field perpendicular to the CuO ₂ layers H _⊥, we observe that the resistivity perpendicular to the layers ρ _⊥ becomes finite at a temperature consistent with previous studies on very similar materials; however, the onset of finite parallel resistivity ρ _∥ occurs at a much higher temperature. This behavior contradicts conventional theory, which predicts that ρ _⊥ and ρ _∥ should become finite at the same temperature. Voltage versus current measurements near the threshold of voltage detectability indicate linear behavior perpendicular to the layers, becoming nonlinear at higher currents, while the behavior is nonlinear from the onset parallel to the layers. These results, in the presence of moderate H _⊥, appear consistent with superconducting order parallel to the layers with voltage fluctuations between the layers due to thermal noise. In search of uncommon effects that might help to explain this behavior, we have performed diffraction measurements that provide evidence for H _⊥-induced charge- and spin-stripe order. The field-induced decoupling of superconducting layers is similar to the decoupled phase observed previously in La _2-xBa _xCuO ₄ with x=1/8 in zero field.