Critical Thickness in Superconducting LaAlO3/KTaO3 (111) Heterostructures

Recently, two-dimensional superconductivity was discovered at the oxide interface between KTaO3 and LaAlO3 (or EuO), whose superconducting transition temperature T-c is up to 2.2 K and exhibits strong crystalline-orientation dependence. However, the origin of the interfacial electron gas, which becomes superconducting at low temperatures, remains elusive. Taking the LaAlO3/KTaO3 (111) interface as an example, we have demonstrated that there exists a critical LaAlO3 thickness of similar to 3 nm. Namely, a thinner LaAlO3 film will give rise to an insulating but not conducting (or superconducting) interface. By in situ transport measurements during growth, we have also revealed that the critical thickness can be suppressed if exposure to oxygen is avoided. These observations, together with other control experiments, suggest strongly that the origination of the electron gas is dominated by the electron transfer that is from oxygen vacancies in the LaAlO3 film to the KTaO3 substrate.

Automated summary

Recent research discovered a critical thickness of around 3 nm for LaAlO3 film on the LaAlO3/KTaO3 (111) interface, beyond which the interface behaves as insulating rather than conducting (or superconducting). In situ transport measurements during growth also revealed that this critical thickness can be suppressed by avoiding exposure to oxygen. These findings suggest that the origin of the electron gas at the interface is dominated by electron transfer from oxygen vacancies in the LaAlO3 film to the KTaO3 substrate.