  Recent breakthroughs in Josephson diodes dangle the possibility of extending
conventional non-reciprocal electronics into the realm of superconductivity.
While a strong magnetic field is recognized for enhancing diode efficiency, it
concurrently poses a risk of undermining the essential superconductivity
required for non-dissipative devices. To circumvent the need for magnetic-based
tuning, we propose a field-effect Josephson diode based on the electrostatic
gate control of finite momentum Cooper pairs in asymmetric
spin-momentum-locking states. We propose two possible implementations of our
gate-controlled mechanism: (i) a topological field-effect Josephson diode in
time-reversal-broken quantum spin Hall insulators; and (ii) semiconductor-based
field-effect Josephson diodes attainable in current experimental setups
involving a Zeeman field and spin-orbit coupling. Notably, the diode efficiency
is highly enhanced in the topological field-effect Josephson diode because the
current carried by the asymmetric helical edge states is topologically
protected and can be tuned by local gates. In the proposed Josephson diode, the
combination of gates and asymmetric spin-momentum-locking nature is equivalent
to that of a magnetic field, thus providing an alternative electrical operation
in designing nonreciprocal superconducting devices.
