Figure 1

(a) $T$ dependence of $\rho$ near the structural and magnetic phase transition. (b) Schematic diagram of the compressed sample. (c) $B$ dependence of $\rho$ in the compressed sample for three principal field directions at $T\sim 0.17\mathrm{K}$. The small magnetoresistance for $B\parallel b$ results from the longitudinal configuration $I\parallel B$. (d) SdH oscillations extracted from the data in (c) as a function of inverse field $1/B$. The curves are vertically shifted for clarity. A third polynomial was fitted to each $\rho (B)$ curve to determine a smoothly varying background ${\rho }_{\mathrm{background}}$ and was subtracted to obtain an oscillatory part ${\rho }_{\mathrm{osc}}$. A normalized quantity ${\rho }_{\mathrm{osc}}/{\rho }_{\mathrm{background}}$ is shown. (e) Fourier transforms of the SdH oscillations in the compressed and elongated samples for selected field directions. The field angle ${\theta }_{ca}$ (${\theta }_{cb}$) is that between the $c$ axis and $B$ in the $ca$ ($cb$) plane. The spectra are vertically shifted for clarity. The two samples give consistent results (compare the elongated-sample spectra at ${\theta }_{ca}=49.5°$ and ${\theta }_{cb}=100.5°$ with the compressed-sample spectra at ${\theta }_{ca}=50.5°$ and $B\parallel b$, respectively).Reuse & Permissions

Figure 2

(a) Angle dependence of the experimental SdH frequencies in the compressed sample. The mark sizes indicate the oscillation amplitudes. The $ca$-plane (blue squares) and $cb$-plane (red circles) data are superimposed. The solid lines indicate the fundamental frequency branches. The dotted lines indicating the harmonic and combination frequencies are calculated from the solid lines. The dashed line, almost overlapped by a solid line, is a fit to the $\gamma$ branch assuming that the responsible FS pocket is an ellipsoid of revolution. The fit gives $k_F^{ab}=0.050{\AA }^{-1}$ and $k_F^c=0.33{\AA }^{-1}$, $k_F^{ab(c)}$ being the Fermi wave number in the $ab$ plane (along the $c$ axis). No frequency other than $3\alpha$ is observed above $F=1\mathrm{kT}$. (b) Comparison between the calculated and experimental frequencies. For the calculated frequencies, both original and adjusted ones are shown (see text). The solid curves representing the experimental frequencies are the same as those in (a). (c) The FS resulting from the original band structure calculation. It consists of a band-68 hole sheet (left) and band-69 electron sheet (right). Since our band structure calculation does not include spin-orbit coupling, it predicts chains of alternating hole and electron pockets along the grey lines, in accord with Ref. 23, but they are so thin that they cannot be drawn accurately. The directions $a$, $b$, and $c$ shown in the figure refer to those of the $Fmmm$ orthorhombic unit cell [15]. (d) The FS in ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ determined in the present study. The drawings of the $\alpha$ hole and $\delta$ electron pockets are based on the adjusted band structure calculation, and the $\gamma$ electron pocket is schematically shown, based on the ellipsoid fit in (a). There might be minute FS pockets along the grey lines, though our data show no trace of such pockets. (e) Electronic band structure near $E_F$ along $\Gamma \Delta FZ$. The $\gamma$ pocket is placed at the position marked by the black arrow (see text).Reuse & Permissions