Strong intervalley mixing between copropagating quantum Hall edge channels in a silicon MOSFET

Copropagating quantum Hall edge channels provide a promising platform for compact electron interferometry and flying quantum states. In silicon, spin-based beam splitters are difficult to implement because the spin-flip scattering required for beam-splitter operation is strongly suppressed by the weak spin–orbit interaction. Therefore, the valley degree of freedom offers a natural alternative to spin-resolved edge channels. Here, we investigate interchannel transitions between copropagating valley edge channels in a double-layer-gated silicon metal–oxide–semiconductor field effect transistor. With the bulk filling factor set to ν = 2, two spin-polarized valley edge channels are brought into close proximity near a depleted side gate. We observe strong intervalley mixing with a transition probability close to 1/2, which is required for realizing a valley beam splitter. In contrast, interchannel transport between edge channels with different spin orientations shows negligible transition probability, consistent with suppressed spin-flip scattering in silicon. These results represent an important step toward compact silicon quantum Hall interferometers based on copropagating valley edge channels.