Electron-tunneling measurements of low-T_c single-layer Bi_2+xSr_2−yCuO_6+δ: Evidence for a scaling disparity between superconducting and pseudogap states

We experimentally study intrinsic tunneling and high magnetic field (up to 65 T) transport characteristics of the single-layer cuprate Bi_2+xSr_2−yCuO_6+δ, with a very low superconducting critical temperature T_c ≲ 4 K. It is observed that the superconducting gap, the collective bosonic mode energy, the upper critical field, and the fluctuation temperature range are scaling down with T_c, while the corresponding pseudogap characteristics remain the same as in high-T_c cuprates with 20 to 30 times higher T_c. The observed disparity of the superconducting and pseudogap scales clearly reveals their different origins.