Bulk electronic structure of optimally doped $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Co}}_x\right)}_2{\text{As}}_2$

We report high-resolution, bulk Compton scattering measurements unveiling the Fermi surface of an optimally doped iron-arsenide superconductor, $\text{Ba}{\left({\text{Fe}}_{0.93}{\text{Co}}_{0.07}\right)}_2{\text{As}}_2$. Our measurements are in agreement with first-principles calculations of the electronic structure, revealing both the $X$-centered electron pockets and the $\Gamma$-centered hole pockets. Moreover, our data are consistent with the strong three dimensionality of one of these sheets that has been predicted by electronic structure calculations at the local-density-approximation-minimum As position. Complementary calculations of the noninteracting susceptibility, ${\chi }_0\left(\mathbf{q},\omega \right)$, suggest that the broad peak that develops due to interband Fermi-surface nesting, and which has motivated several theories of superconductivity in this class of material, survives the measured three dimensionality of the Fermi surface in this family.

Figure 1

(Color online) (a) The LDA FS of $\text{Ba}{\left({\text{Fe}}_{0.93}{\text{Co}}_{0.07}\right)}_2{\text{As}}_2$ (top) and its relation to the occupation density projected down the $c^{\ast }$ axis (bottom). Note that the occupation density has been convoluted with the experimental resolution function. (b) The overlaid FS contours (black and white lines, top) are identified via the maxima in (the absolute value of) the first derivative of the occupation density shown at the bottom along a projected, high-symmetry path.

Figure 2

(Color online) The occupation density of $\text{Ba}{\left({\text{Fe}}_{0.93}{\text{Co}}_{0.07}\right)}_2{\text{As}}_2$ from (a) experimental Compton scattering measurements at 295 K and (b) the electronic structure calculations of Fig. 1a from the original calculation (top) and after rigidly shifting the bands (see text, bottom). The first derivative of the experimental data is shown in (c) in the same way as in Fig. 1b. In (d) the FS corresponding to the shifted bands is shown for comparison with Fig. 1a.

Figure 3

(Color online) The real and imaginary parts of the static susceptibility, $\chi \left(\mathbf{q},0\right)$, of $\text{Ba}{\left({\text{Fe}}_{0.93}{\text{Co}}_{0.07}\right)}_2{\text{As}}_2$. The wave vector $\mathbf{q}$ is expressed in units of $2\pi /a$.