M. Oda et al., STM IMAGES OF A SUPERCONDUCTING CU-O PLANE AND THE CORRESPONDING TUNNELING SPECTRUM IN BI2SR2CACU2O8+DELTA, Physical review. B, Condensed matter, 53(5), 1996, pp. 2253-2256
Clear atomic images of Bi2Sr2CaCu2O8+delta cleaved surfaces have been
observed at T=6 and 300 K by scanning tunneling microscopy (STM). The
atomic images taken for bias voltages much lower than the Bi-O plane s
emiconducting gap E(g) similar to 100 meV, corresponding to the Cu-O p
lane, indicate that the conduction electrons exist mainly in the Cu 3d
(x2-y2) and O 2p(sigma) orbitals. Tunneling spectra have been also mea
sured in the same processes as in the Cu-O plane STM image observation
s at T=6 K. The low-temperature spectra are in good agreement with tha
t in a d-wave superconductor with an anisotropic Fermi surface on whic
h the normal density of states N(k(F)) is largest (N-max) for the maxi
mum gap directions and decreases to similar to N-max/2 for the node di
rections. This, combined with the result on the N(k(F)) anisotropy in
photoemission experiments, is consistent with a d(x2-y2) superconducti
ng gap.