  The gate-voltage-induced suppression of critical currents in metallic
superconductors observed recently [De Simoni et al., Nat. Nanotechnol. 13, 802
(2018)] has raised crucial questions regarding the nature and mechanism of the
electric field effect in these systems. Here, we demonstrate an enhancement of
up to 30 % in critical current in the type II superconductor NbN, micro- and
nano superconducting bridges, tunable via a back-gate voltage. Our suggested
plausible mechanism of this enhancement in critical current based on surface
nucleation and pinning of Abrikosov vortices is consistent with expectations
and observations for type-II superconductor films with thicknesses comparable
to their coherence length. Furthermore we demonstrate infinite
electroresistance and a hysteretic resistance dependence on the applied
electric field which could lead to logic and memory applications in a
superconductors-based low-dissipation digital computing paradigm. Our work thus
provides the first demonstration of an electric field enhancement in the
superconducting property in metallic superconductors, constituting a crucial
step towards understanding of electric field-effects on the fundamental
properties of a superconductor and its exploitation for future technologies.
