Persistent Photoconductivity And Magnetoresistance In Yba2cu3o6.34 Thin Film

We have used persistent photoconductivity to smoothly tune the hole-doping in an under doped cuprate in the critical doping region and studied its transverse magnetoresistance (MR). A series of YBa2Cu3O6+x (0.02 <= x <= 1) thin films of thickness similar to 50 nm were grown by sputtering and the oxygen contents were estimated from the c-axis lattice constant. The film YBa2Cu3O6.34, with composition at the critical doping regime for the insulator-metal-superconductor transition (T-C < 0.13 K), was chosen for studying persistent photoconductivity and MR. The sample was illuminated at 0.8 K using an ultraviolet stroboscope with wavelength range of 220-700 nm for several hours. Resistivity down to 0.13 K and MR in a field up to 9T were measured in intermittent stages. The sample resistance was found to decrease exponentially with the illumination time. The field dependence of MR changed from quadratic to linear behavior after shining light on the sample for similar to 13h. This cross-over in the field dependence of transverse MR clearly shows that the topology of the Fermi surface was changed drastically by shining light. Our observations suggest a pseudogap state as a precursor of superconductivity in YBa2Cu3O6 broken vertical bar x