An Ambipolar Superconducting Field‐Effect Transistor Operating above Liquid Helium Temperature

Abstract Superconducting (SC) devices are attracting renewed attention as the demands for quantum‐information processing, meteorology, and sensing become advanced. The SC field‐effect transistor (FET) is one of the elements that can control the SC state, but its variety is still limited. Superconductors at the strong‐coupling limit tend to require a higher carrier density when the critical temperature (T_C) becomes higher. Therefore, field‐effect control of superconductivity by a solid gate dielectric has been limited only to low temperatures. However, recent efforts have resulted in achieving n‐type and p‐type SC FETs based on organic superconductors whose T_C exceed liquid He temperature (4.2 K). Here, a novel “ambipolar” SC FET operating at normally OFF mode with T_C of around 6 K is reported. Although this is the second example of an SC FET with such an operation mode, the operation temperature exceeds that of the first example, or magic‐angle twisted‐bilayer graphene that operates at around 1 K. Because the superconductivity in this SC FET is of unconventional type, the performance of the present device will contribute not only to fabricating SC circuits, but also to elucidating phase transitions of strongly correlated electron systems.