the nominal charge of the TaO$_2$ layer is +1 and that of the KO layer is -1 (BaO and HfO$_2$ layers are neutral.). One possible way would be substituting K atoms with Ba in the KO layer. In this case, the Rashba strength remains still large ($\alpha_R \approx 0.2$ eVÅ) in the lower $d_{xz/yz}$ bands (Fig. \[fig:tao2bho\]a), while the Rashba splitting in the upper $d_{xz/yz}$ bands is greatly suppressed largely because the Ba substitution reduces by 70% the height difference of Ta and O atoms in the TaO$_2$ layer. Once again, the considerable band splitting along $\mathrm{X}$–$\mathrm{M}$ ($\approx 24$ meV) and AM texture at $E_{vH}$ in Fig \[fig:tao2bho\] are contrary to the prediction of the $t_{2g}$-only TB model (see Appendix C and Fig. A1), and hence demonstrate that inclusion of the $e_g$ manifold is essential in understanding the Rashba-Dresselhaus splitting. We expect that partial chemical substitution (TaO$_2$/K$_{1-x}$Ba$_{x}$O layer on BHO) could induce the 2DEG in the TaO$_2$ layer in experiments. At $x=1$, [*i.e.*]{}, 100% Ba substitution, the Fermi level lies slightly above the VHS (Fig. \[fig:tao2bho\]a), which means we can access the VHS at $x \lesssim 1$. We expect the qualitative features of our Rashba-Dresselhaus splitting to be generic for 