Gate-tunability of the superconducting state in EuO/KTaO₃ (111) interface

The recent discovery of superconducting interfaces in the KTaO₃ (111)-based heterostructures is intriguing, since a much higher superconducting critical temperature (T_C; ~ 2 K) is achieved compared to that in the SrTiO₃ heterostructures (~ 300 mK). In this work, we report the superconducting properties of EuO/KTaO₃ (111) interface as a function of the interface carrier density (n_s) tuned by varying the EuO growth condition and by applying a back gate on the KTaO₃ crystals. The T_C reaches its maximum of 2 K with n_s ~ 1×10¹⁴ cm^-2. As n_s varies, the critical current density (J_C) exhibits a trend similar to that of T_C, while the upper critical magnetic field (B_C2) exhibits the opposite trend. The opposite trends between B_C2 and T_C in the underdoped region are similar to the characteristics of high temperature superconducting cuprates, suggesting a relatively stronger Cooper pairing potential at lower n_s. Our results could pave the way for the further understanding the pairing mechanisms of superconductivity interfaces in the KTaO₃ (111) heterostructures.