Critical Thickness in Superconducting LaAlO 3 / KTa O 3 ( 111 ) Heterostructures

Yanqiu Sun, Yuan Liu, Siyuan Hong, Zheng Chen, Meng Zhang, and Yanwu Xie

Recently, two-dimensional superconductivity was discovered at the oxide interface between ${\mathrm{KTaO}}_3$ and ${\mathrm{LaAlO}}_3$ (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 ${\mathrm{LaAlO}}_3/{\mathrm{KTaO}}_3\left(111\right)$ interface as an example, we have demonstrated that there exists a critical ${\mathrm{LaAlO}}_3$ thickness of $\sim 3\mathrm{nm}$. Namely, a thinner ${\mathrm{LaAlO}}_3$ 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 ${\mathrm{LaAlO}}_3$ film to the ${\mathrm{KTaO}}_3$ substrate.

Phys. Rev. Lett. 127, 086804

The published article is available at https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.086804