Extreme Fermi surface smearing in a maximally disordered concentrated solid solution*

The impact of extreme chemical disorder on the Fermi surface of the equiatomic alloy Ni_0.25Fe_0.25Co_0.25Cr_0.25 was probed by high-resolution X-ray Compton scattering. Such experiments probe the Fermi surface via the occupied momentum states, meaning that such measurements are ideally suited to revealing the electronic structure of such disordered alloys. The smearing of the Fermi surface is rather strong, reaching up to 40% of 2π/a, but nevertheless a Fermi surface can be clearly identified in the experimental data and the extent of the smearing and its variation on and across different sheets has been investigated. By connecting this smearing with the coherence length of the quasiparticle states, estimates of the electronic mean-free-path and residual resistivity have been made. It is found that the mean-free paths are in the range 0.7 - 0.9 nm.