Confining electronic states with domain walls in ferroelectric SnTe monolayers*

Electronic standing wave patterns at surfaces are usually generated by edges, atomic steps or adatoms that introduce large potential barriers. However, in multi-valley semiconducting 2D materials, quasiparticle confinement and suppressed transmission can be created from mismatched electronic structures through domain walls, with a neglectable built-in bias at the interface. Here, we report the first observation of electronic standing waves near the valence band maximum in a SnTe monolayer that is generated by the reflection from ferroelectric domain walls. Despite of the nearly flat potential barrier at the domain walls, the reflectivity is found to be 68+-9% at 4.7 K, and no sign of transmission was seen. Such a strong confinement of electronic states is due to a large change of valley positions between the neighboring domains arising from a 90 degree rotation of the Brillouin zone. These results show potential for polarization-tuned valleytronics in 2D ferroelectrics.