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 ${\mathrm{Ni}}_{0.25}{\mathrm{Fe}}_{0.25}{\mathrm{Co}}_{0.25}{\mathrm{Cr}}_{0.25}$. 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 $2\pi /a$). The extent of this smearing and its variation on and between different sheets of the Fermi surface have 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.

Figure 1

Logarithm of the Bloch spectral function of NiFeCoCr calculated within the KKR-CPA-DLM framework.

Figure 2

Occupation $n(\mathbf{k})$ in the (001) plane through $\mathrm{\Gamma }$, showing the KKR-CPA-DLM theory (top) and experiment (bottom). $2\pi /a\approx 0.93$ a.u., and the white lines indicate the isodensities associated with the three FS sheets.

Figure 3

Bloch spectral function $A_B(E=E_F,\mathbf{k})$ in the (001) plane through $\mathrm{\Gamma }$ from the KKR-CPA-DLM theory (top), with the absolute square of the gradient of the experimental data (bottom). The BZ and some symmetry points are also plotted.

Figure 4

The hole (top) and two electron (middle and bottom) FS sheets of NiFeCoCr obtained from the Compton experiment. These surfaces are the isodensities (0.5, 1.5, and 2.5) plotted from the reconstructed occupation number. The color shows the variation of the quasiparticle coherence length $\xi$ (in Å) across the FS extracted from the smearing. The wireframe box is the first Brillouin zone.

Figure 5

Occupation $n(\mathbf{k})$ from the experiment (filled circles) along the [100] (top) and [110] (bottom) directions in the BZ (where $k$ is in units of $2\pi /a$). $n(\mathbf{k})$ has been fitted with the sum (black line) of three tanh functions (red dotted line, green dashed-dotted line, and blue dashed line). The edge of the BZ is at 1.00 and 1.06 for the [100] and [110] directions, respectively, and symmetry points such as $\mathrm{\Gamma }$, $K$, and $X$ are shown.