Tuning Kinetic Inductance with Doping in Superconducting Electron Gases at the KTaO₃ (111) Interface

We used coplanar waveguide resonators fabricated from the two-dimensional superconductor formed at KTaO₃ (111) interfaces to characterize the superconductor's sheet kinetic inductance L_K/□. Upon varying the carrier density, in samples with T_c ranging from 0.62 to 1.81 K, we can tune L_K/□ between 1.88 and 7.42 nH/□ at the lowest temperatures, exceeding the highest values reported for granular aluminum films. The temperature dependence of L_K/□ is consistent with a superconducting gap without nodes. The high L_K/□ of superconducting KTaO₃ (111) interfacial electron gases combined with the high dielectric constant of KTaO₃ results in resonators with exceedingly low phase velocities ("slow light") and small mode volumes. In addition, superconducting KTaO₃ (111) interfacial electron gases are robust in magnetic fields well above a Tesla. These features can enable unique device applications in superconducting electronics and quantum information science.