Valley-Polarized Interlayer Conduction of Anisotropic Dirac Fermions in SrMnBi$_{2}$

We report anisotropic Dirac fermions in a Bi square net of SrMnBi$_{2}$ and their valley-selective interlayer conduction under in-plane magnetic fields. In contrast to the commonly-observed isotropic Dirac Fermi surfaces, the Dirac Fermi surface in SrMnBi$_{2}$ is highly anisotropic with strong momentum-dependence of Fermi velocity as well as interlayer coupling. The resulting $c$-axis resistivity exhibits clear angular magnetoresistance oscillations indicating coherent interlayer conduction. Strong fourfold variation of the coherent peak in the $c$-axis resistivity reveals that the contribution of each Dirac valley is significantly modulated by the in-plane field orientation. Furthermore, we found a signature of broken valley symmetry at high magnetic fields. These findings demonstrate that a quasi-two-dimensional anisotropic Dirac system can host a valley-polarized interlayer current through magnetic valley control.