High mobility electron gas with quasi-two-dimensional characteristics at the interface of Cr₂O₃/SrTiO₃ heterostructures

Two-dimensional electron gas is precisely confined at the interface of insulating oxide thin films and substrates, e.g., LaAlO₃/SrTiO₃(STO) and, thus, shows 2D electronic transport features. Here, we report a high mobility electron state at the interface of a Cr₂O₃ film and a STO substrate, which is realized by depositing a Cr film onto a STO (111) substrate in high vacuum (1 × 10⁻¹⁰ mbar) using molecular beam epitaxy. At a substrate temperature of 700 °C, the deposited Cr films capture oxygen atoms from STO substrates, resulting in the formation of an insulating Cr₂O₃ layer and an oxygen-deficient STO layer. Due to the presence of high mobility electrons [1.5 × 10⁴ cm²V⁻¹s⁻¹ at 1.8 K] at the Cr₂O₃/STO interface, both out-of-plane and in-plane Shubnikov-de Haas oscillations are observed at low temperatures (<3 K), which suggests that the highly conducting electron gas has extended into the STO bulk along the thickness direction with a certain depth to allow electrons to complete the cyclotron motion.