Superconducting Transition Temperature Modulation in NbN via EDL Gating

TL;DR

This study demonstrates reversible modulation of the superconducting transition temperature in NbN thin films using electric double-layer gating with high surface charge densities, revealing effects beyond simple screening models.

Contribution

It introduces an efficient polymer electrolyte gating method to modulate superconductivity in NbN, showing effects that challenge traditional screening explanations.

Findings

Reversible Tc modulation achieved with high surface charge densities.

Sign of Tc change depends on gate voltage polarity.

Modulation effects exceed predictions of simple screening models.

Abstract

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 $\approx 2.8 \times 10^{15}\,\mathrm{cm}^{-2}$ 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\"ive screening model.