A clean ballistic quantum point contact in strontium titanate

The perovskite oxide strontium titanate (SrTiO3) combines electrostatic tunability, superconductivity and spin–orbit coupling, and is of potential use in the development of quantum devices. However, exploring quantum effects in SrTiO3 nanostructures is challenging because of the presence of disorder. Here we report high-mobility, gate-tunable devices in SrTiO3 that have ballistic constrictions and clean normal-state conductance quantization. Our devices are based on SrTiO3 two-dimensional electron gas channels that have a thin hafnium oxide barrier layer between the channel and an ionic liquid gate. Conductance plateaus show twofold degeneracy that persists for magnetic fields of at least 5 T. This is above what is expected from the g factors extracted at high fields and could be a signature of electron pairing extending outside the superconducting regime