Fig. 3.

a, b Distribution of the photoconductivity ${\mathit{\sigma }}_{\mathit{xx}}^{\mathit{x}}$ in the first Brillouin zone. Without including the spin-orbit coupling (SOC), the k to −k symmetry appears while finite SOC breaks such a symmetry. The ring-like shape indicates the resonant optical transition between valence (E_l) and conduction (E_n) bands by the selection rule E_n − E_l = ħω (1.2 eV). c Transitions from top two valence bands to the bottom two conduction bands. The yellow rings indicate the transition paths and correspond to the large-${\sigma }_{xx}^x$-amplitude rings in (b)