Electronic and structural effects of oxygen doping in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{x}}$ superconductors characterized by tunneling microscopy

Scanning tunneling microscopy has been used to characterize the electronic and structural effects of oxygen doping in ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathit{x}}$ materials. Bias-voltage-dependent images of oxygen-deficient nonsuperconducting crystals show that reversible oxygen loss leads to nonperiodic variations in the electronic states near the Fermi level (±300 mV). Variations in the electronic states near the Fermi level are not observed, however, in images of superconducting samples. In addition, high-resolution images of the BiO layer of oxygen-deficient samples do not exhibit vacancies or strongly perturbed sites, but rather appear similar to images of the BiO layer of superconducting crystals. These data indicate that suppression of ${\mathit{T}}_{\mathit{c}}$ in ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathit{x}}$ may not be due to oxygen loss from the BiO layer.