title: Gap function with point nodes in borocarbide superconductor YNi2B2C.
abstract: To determine the superconducting gap function of YNi2B2C, the c-axis thermal conductivity kappa(zz) was measured in H rotated in various directions. The angular variation of kappa(zz) in H rotated within the ab plane shows a peculiar fourfold oscillation with narrow cusps. The amplitude of this fourfold oscillation becomes very small when H is rotated conically around the c axis with a tilt angle of 45 degrees. These results provide the first compelling evidence that the gap function has point nodes located along the a and b axes. This unprecedented gap structure challenges the current view on the pairing mechanism.
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Izawa
authors.forename: K
authors.initials: K
authors.lastname: Kamata
authors.forename: Y
authors.initials: Y
authors.lastname: Nakajima
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuda
authors.forename: T
authors.initials: T
authors.lastname: Watanabe
authors.forename: M
authors.initials: M
authors.lastname: Nohara
authors.forename: H
authors.initials: H
authors.lastname: Takagi
authors.forename: P
authors.initials: P
authors.lastname: Thalmeier
authors.forename: K
authors.initials: K
authors.lastname: Maki