Nesting Properties and Anisotropy of the Fermi Surface ofLuNi2B2C

The rare-earth nickel borocarbides, with the generic formula $R{\mathrm{Ni}}_2{\mathrm{B}}_2\mathrm{C}$, have recently been shown to display a rich variety of phenomena. Most striking has been the competition between, and even coexistence of, antiferromagnetism and superconductivity. We have measured the Fermi surface (FS) of ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}$, and shown that it possesses nesting features capable of explaining some of the phenomena experimentally observed. In particular, it had previously been conjectured that a particular sheet of FS is responsible for the modulated magnetic structures manifest in some of the series. We report the first direct experimental observation of this sheet.