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Gap Function with Point Nodes in Borocarbide Superconductor YNi_2B_2C

K. Izawa·K. Kamata·Y. Nakajima·Y. Matsuda·T. Watanabe·M. Nohara·H. Takagi·P. Thalmeier·K. Maki
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Abstract

To determine the superconducting gap function of a borocarbide superconductor YNi_2B_2C, the c-axis thermal conductivity kappa_zz was measured in a magnetic field rotated in various directions relative to the crystal axes. 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. Based on these results, we provide the first compelling evidence that the gap function of YNi_2B_2C has POINT NODES, which are located along the [100] and [010]-directions. This unprecedented gap structure challenges the current view on the pairing mechanism and on the unusual superconducting properties of borocarbide superconductors.

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K. Izawa, K. Kamata, Y. Nakajima, Y. Matsuda, T. Watanabe, M. Nohara, H. Takagi, P. Thalmeier, K. Maki. 2002-05-09. Gap Function with Point Nodes in Borocarbide Superconductor YNi_2B_2C. https://doi.org/10.1103/physrevlett.89.137006

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