Fermi Surface Nesting in Disordered Cu1xPdx Alloys

The concentration-dependent position of the diffuse peaks in electron and x-ray diffraction patterns of Cu12xPdx alloys in the disordered state is attributed to Fermi surface nesting. We present the first experimentally determined Fermi surfaces of Cu0.72Pd0.28 and Cu0.6Pd0.4, and show that they do indeed possess significant flat areas capable of nesting. Moreover, the magnitudes of the nesting vectors are in excellent agreement with those deduced from electronic structure calculations and diffraction experiments. The shape of the Fermi surface (FS) often results in a variety of ordering phenomena in metals. These arise because of large areas of parallel or near-parallel sheets of FS which can “nest” with each other, resulting in a significant enhancement of those electronic excitations with a wave vector q which spans the parallel sections. Spin- and charge-density waves [1] are two examples of FS-driven orderings, where the periodicity of the modulation of the conduction electrons is determined by a nesting vector on the FS. The study of the short-range compositional order found in many binary metallic alloys above the order-disorder transition temperature (Tc provides valuable insight into the phase behavior of these systems [2,3]. The origin of the short-range order (SRO) often lies in a nestable FS, in a manner analogous to the way nesting may yield a paramagnetic state susceptible to magnetic order. Indeed, it was just this idea that led Moss to suggest that measurements of the diffuse scattering in x-ray and electron diffraction patterns could be used to make inferences about the FS topology of disordered alloys [4].