STM STUDIES OF ELECTRONIC ORDER IN THE UNDERDOPED SURFACE OF YBa2Cu3Oy

To study the nanoscale electronic order in high-T c superconductors, we have performed low-temperature scanning tunneling microscopy (STM) experiments on YBa 2 Cu 3 O y, single crystals. The electronic state of the underdoped CuO 2 plane is studied through the BaO surface taking advantage of the cleaved surface, which has an insufficient carrier doping into the topmost CuO 2 plane because of the incomplete carrier reservoir. The STM image measured at low bias-voltage below 20 mV shows the one-dimensional (1D) electronic modulation along the Cu - O bonds. The 1D modulation do not have long-range order and the periodicity varies within the range ~ 2a - 4a depending on the position on the surface. These results indicate that electronic order in underdoped YBa 2 Cu 3 O y, differs from the 4a×4a checkerboard structure observed in Bi 2 Sr 2 CaCu 2 O y and Ca 2-x Na x CuO 2 Cl 2.