Ultrahigh-resolution photoemission spectroscopy of Ni borocarbides: direct observation of the superconducting gap and a change in gap anisotropy by impurity
We have performed ultrahigh-resolution photoemission spectroscopy of Y(Ni1-xPtx)2B2C ( x = 0.0 and 0.2) in order to study the changes in the density of states across the superconducting transition. Because of a drastic increase in energy resolution, we clearly observe the opening of superconducting gaps across T(c) in both compounds. Furthermore, we find a small but significant difference in the superconducting-state spectral shape. This can be explained in terms of reduction in gap anisotropy by introducing impurities and provides spectroscopic evidence for an anisotropic s-wave gap in YNi2B2C.
Yokoya
T
Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
Kiss
T
Watanabe
T
Shin
S
Nohara
M
Takagi
H
Oguchi
T