Extreme Fermi surface smearing in a maximally disordered concentrated solid solution

We show that the Fermi surface can survive the presence of extreme compositional disorder in the equiatomic alloy Ni\(_{0.25}\)Fe\(_{0.25}\)Co\(_{0.25}\)Cr\(_{0.25}\). Our high-resolution Compton scattering experiments reveal a Fermi surface which is smeared across a significant fraction of the Brillouin zone (up to 40\% of \(\frac{2\pi}{a}\)). The extent of this smearing and its variation on and between different sheets of the Fermi surface has been determined, and estimates of the electron mean-free-path and residual resistivity have been made by connecting this smearing with the coherence length of the quasiparticle states.