Electronic structure of detwinned BaFe${}_2$As${}_2$ from photoemission and first principles

We performed angle-resolved photoelectron spectroscopy (ARPES) studies on mechanically detwinned BaFe${}_2$${\mathrm{As}}_2$. We observe clear band dispersions, and the shapes and characters of the Fermi surfaces are identified. Shapes of two-hole pockets around the $\Gamma$ point are found to be consistent with the Fermi surface topology predicted in the orbital ordered states. Dirac-cone-like band dispersions near the $\Gamma$ point are clearly identified as theoretically predicted. At the$X$ point, split bands remain intactdespite detwinning, barring a twinning origin of the bands. Observed band dispersions are compared with calculated band structures. With a magnetic moment of 0.2 $\mu$${}_B$ per iron atom, there is good agreement between the calculation and the experiment.

Figure 1

(a) Sample holder designed to apply strain (or stress) to samples. (b) Constant energy map at the Fermi level. Optical microscopy images of (c) detwinned and (d) twinned samples with a polarized light source. Images were taken at 88 K. The black arrow marks a twin boundary. (e) Raw ARPES data along the $\Gamma$-$X$ direction; (f) its second derivative. (g, h) Band dispersions along different cuts as indicated in (b).

Figure 2

(a) Fermi surface map around the $\Gamma$ point. (b–d) Second derivatives of ARPES data along cuts indicated by dashed lines in (a). (e) Fermi surface map around the $X$ point. (f–h) Band dispersions from second derivatives of the data along cuts indicated by dashed lines in (e). (i) Characters of the Fermi surface pockets. Red and blue circles indicate hole and electron pockets, respectively. Inset: Shape of the two-hole pockets around the $\Gamma$ point and definition of the angle ($\theta$) used in Fig. 4.

Figure 3

(a–c) Band dispersions along three high-symmetry lines, $\Gamma$-$X$, $\Gamma$-$Y$, and $\Gamma$-$M$, overlain with calculated bands with a magnetic moment of 0.2 $\mu$${}_B$. The As height was adjusted for the best fit and is larger by 0.070 Å${}^{-1}$ than the experimentally obtained value. (d–f) Bands calculated with the experimentally obtained As height. Calculated bands were renormalized by a factor of 3 and the Fermi level was shifted by 25 meV.

Figure 4

(a) MDCs at different binding energies. (b) Fitting results for MDCs from above (UB), at (DP), and below (LB) the Dirac point.