Quasiparticle interference and superconducting gap in Ca
Na
CuO
Cl
Hanaguri, Tetsuo*; Kosaka, Yuki*; Davis, J. C.*; Lupien, C.*; Yamada, Ikuya*; Azuma, Masaki*; Takano, Mikio*; Oishi, Kazuki; Ono, Masaki*; Takagi, Hidenori*
High-transition-temperature (high-
) superconductivity is ubiquitous in the cuprates containing CuO
planes, but each cuprate has its own character. The study of the material dependence of the
-wave superconducting gap (SG) should provide important insights into the mechanism of high-
superconductivity. However, because of the "pseudogap" phenomenon, it is often unclear whether the energy gaps observed by spectroscopic techniques really represent the SG. Here, we use scanning tunnelling spectroscopy to image nearly optimally doped Ca
Na
CuO
Cl
(Na-CCOC) with
K. It enables us to observe the quasiparticle interference effect in this material, through which we obtain unambiguous information on the SG. Our analysis of quasiparticle interference in Na-CCOC reveals that the SG dispersion near the gap node is almost identical to that of Bi
Sr
CaCu
O
(Bi2212) at the same doping level, despite the
of Bi2212 being three times higher than that of Na-CCOC. We also find that the SG in Na-CCOC is confined in narrower energy and momentum ranges than Bi2212, which explains
at least in part
the remarkable material dependence of
.