On the Anisotropy of the Superconducting Order Parameter of Cu Oxides Observed by STM/STS

a−bPlane Anisotropy of the Superconducting Gap inBi2Sr2<

“…1, the so-called zero-bias conductance peak (ZBCP) structure [17] was observed along the [100] direction, and a clear superconducting gap structure was observed along the [110] direction. The ZBCP structure was reported also by other groups for the tunneling spectroscopy measurements on high-T c cuprates [5][6][7][18][19][20]. It is claimed that the ZBCP is due to line nodes on the Fermi surface of the d-wave superconducting gap [17,[21][22][23].…”

“…According to these theories, these results seem to suggest the d xy -wave gap and be inconsistent with the results along the directions intermediate between [100] and [110] at first sight. However, these curves observed along the [100] and [110] directions are also explained by the d x 2 2y 2 -wave gap, taking into account the electron orbital in the periodic arrangement of surface oxygen atoms in the Cu-O plane [6]. This was already discussed in detail in our previous paper [14].…”

“…Many of them suggest that the superconducting gap of high-T c cuprates has the d-wave symmetry. However, in the scanning tunneling microscope (STM) spectroscopy method, by which one can observe the electronic density of states directly with high resolution in energy, various results were reported [5][6][7][8][9][10][11][12], and those results have not converged yet. We reported that the superconducting gap is highly anisotropic in Bi 2 Sr 2 CaCu 2 O 8 from STM spectroscopy measurements on single crystals [13].…”

Theory of Josephson effects in anisotropic superconductors

“…31 On the other hand, the existence of zero-bias conductance peaks ͑ZBCP's͒ at the surface of high-T c superconductors has been confirmed by several tunneling spectroscopy measurements. [32][33][34][35][36][37][38][39][40] It has been revealed based on a tunneling theory [41][42][43] that the experimental ZBCP's are closely related to the ZES's at the surface of d-wave superconductors. These ZES's are induced for the reason that the pair potential in high-T c superconductors incurs a change in sign in some region of the Fermi surface.…”

STM images of a superconducting Cu-O plane and the corresponding tunneling spectrum inBi2Sr2Oda1, Manabe2, Ido3 1996Phys. Rev. B845160View full textAdd to dashboardCite

“…On the other hand, Tanaka et al have recently proposed a model that electron tunneling occurs mainly from the O 2p orbitals on the surface Cu-O plane and reported that based on the model the observed gap anisotropy is consistent with a d x 2 Ϫy 2 gap. 21 Angle-resolved photoemission and Raman scattering experiments in Bi2212 have also shown a significant gap anisotropy consistent with d x 2 Ϫy 2 symmetry. 22,23 Recent angle-resolved photoemission experiments have reported an extended s-wave symmetry in which a small finite gap ⌬ s exists for the 45°off-axis directions and nodes are located at both sides of these axes.…”