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.