Superconducting Transition Temperature Modulation in NbN via EDL Gating

We perform electric double layer gating experiments
on thin films of niobium nitride. Thanks to
a cross-linked polymer electrolyte system of improved
efficiency, we induce surface charge densities as high as
? 2.8 × 1015cm?2 in the active channel of the devices.
We report a reversible modulation of the superconducting
transition temperature (either positive or negative
depending on the sign of the gate voltage) whose magnitude
and sign are incompatible with the confinement of
the perturbed superconducting state to a thin surface
layer, as would be expected within a na¨?ve screening
model