Electrostatic Field-Driven Supercurrent Suppression in Ionic-Gated Metallic Superconducting Nanotransistors

Abstract

Recent experiments have shown the possibility of tuning the transport properties of metallic nanosized superconductors through a gate voltage. These results renewed the longstanding debate on the interaction between electrostatic fields and superconductivity. Indeed, different works suggested competing mechanisms as the cause of the effect: an unconventional electric field-effect or quasiparticle injection. Here, we provide conclusive evidence for the electrostatic-field-driven control of the supercurrent in metallic nanosized superconductors, by realizing ionic-gated superconducting field-effect nanotransistors (ISFETs) where electron injection is impossible. Our Nb ISFETs show giant suppression of the superconducting critical current of up to ∼45%. Moreover, the bipolar supercurrent suppression observed in different ISFETs, together with invariant critical temperature and normal-state resistance, also excludes conventional charge accumulation/depletion. Therefore, the microscopic explanation of this effect calls upon a novel theory able to describe the nontrivial interaction of static electric fields with conventional superconductivity.

Destroying superconductivity in thin films with an electric field

“…Without any further assumption or fitting parameter, we found that: i) consistent with an EFT approach, parametrically small corrections to the electric permittivity are sufficient to drive a phase transition and to match the measured behavior of the critical current as a function of the applied electric field, ii) the qualitative behaviour is independent of the charge sign of the electrodes, iii) the critical temperature is not appreciably affected by the electric field applied, iv) the effect vanishes when the thickness of the sample is increased over several coherence lengths. All these predictions are both qualitatively and quantitatively in agreement with the experiments [2,5,6,12,[16][17][18][19]. Additionally, we have proposed a way to further test our theoretical model through elec-tron tunneling, highlighting the features that could be detected in these kind of experiments.…”

“…These include electric-field induced spin-orbit polarization [13], Rashba-like surface effects [14] and the excitation of an exotic superconducting state due to Schwinger-like effects [15]. All these proposals lead to a weakening of superconductivity but they do not fully explain other experimental results [2,12,[16][17][18][19] .…”

“…It has been suggested that energetic quasi-particle injection from the gate control [6,7] or energy or phase fluctuations [9] could be responsible for the observations. These ideas seem to be precluded by recent ionic-gating experiments, where the electric field is generated by crystallised charges [12], as there is no moving charge.…”

Signatures of gate-driven out of equilibrium superconductivity in Ta/InAs nanowires

“…In the recent years, suppression of supercurrent by applying a voltage to a gate electrode in the vicinity of superconducting metallic nanowire has attracted much attention as a promising building block for highly scalable superconducting switches . In some works, the effect is attributed to the large electric field (10 8 V/m) at the superconducting surface [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], which distorts the superconducting state and leads to the quenching of the superconductivity [29][30][31][32][33]. Other studies [22][23][24][25][26][27][28] reported a correlation between the gate controlled supercurrent (GCS) and the leakage current flowing between the gate and the superconducting device.…”

Reversible tuning of superconductivity in ion-gated niobium nitride ultrathin films by self-encapsulation with a high-$κ$ dielectric layer

“…The ionic gating technique is a very powerful tool to tune the properties of a large variety of materials, including high-carrier density systems such as metals [1][2][3][4][5][6], BCS superconductors [7][8][9][10][11], thin flakes of metallic transitionmetal dichalcogenides [12][13][14] and iron-based superconductors [15][16][17][18][19][20][21] using a field-effect transistor (FET) configuration. In principle, the basic mechanism by which it operates is electrostatic and fully reversible: when the interface between an electrolyte and the material under study is polarized by a gate voltage, the mobile ions accumulate in the so-called electric double layer (EDL) and build up electric fields up to ∼ 100 times larger than those achievable in standard solid-dielectric FETs [22,23].…”