Nesting properties and anisotropy of the Fermi surface of LuNi2B2C

The rare-earth nickel borocarbides, with the generic formula RNi2B2C, have recently been shown to display a rich variety of phenomena. Most striking h as been the competition between, and even coexistence of, antiferromagnetis m and superconductivity. We have measured the Fermi surface (FS) of LuNi2B2 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 modul ated magnetic structures manifest in some of the series. We report the firs t direct experimental observation of this sheet.