Unveiling Mechanisms of Electric Field Effects on Superconductors by Magnetic Field Response

Abstract

We demonstrate that superconducting aluminium nano-bridges can be driven into a state with complete suppression of the critical supercurrent via electrostatic gating. Probing both in-and out-of-plane magnetic field responses in the presence of electrostatic gating can unveil the mechanisms that primarily cause the superconducting electric field effects. Remarkably, we find that a magnetic field, independently of its orientation, has only a weak influence on the critical electric field that identifies the transition from the superconducting state to a phase with vanishing critical supercurrent. This observation points to the absence of a direct coupling between the electric field and the amplitude of the superconducting order parameter or 2π-phase slips via vortex generation. The magnetic field effect observed in the presence of electrostatic gating is well described within a microscopic scenario where a spatially uniform inter-band π-phase is stabilized by the electric field. Such an intrinsic superconducting phase rearrangement can account for the suppression of the supercurrent, as well as for the weak dependence of the critical magnetic fields on the electric field.

Gate-controlled Suspended Titanium Nanobridge Supercurrent Transistor

“…4a), corresponding to a conductance of ∼ 10 −13 Ω −1 , and the current is lower than ∼ 1.5 pA in the full range of the applied voltage. We stress that such a value is comparable with those obtained in previous experiments performed on non-suspended devices set on sapphire substrates [1,9,16,17], thereby suggesting that most of the measured leakage current is likely to be dispersed through the wiring setup.…”

“…In a family of experiments [1,2] carried on all-metallic supercurrent nano-transistors a surprising gating effect has been recently shown. These include the full suppression of the critical supercurrent [1,[3][4][5][6], the increase of quasiparticle population [7], the manipulation of the superconducting phase [8], and the broadening of the switching current distributions [9]. Aside from the high potential for future applications [2], these findings raised fundamental questions on the origin of these phenomena [10].…”

“…Aside from the high potential for future applications [2], these findings raised fundamental questions on the origin of these phenomena [10]. To date, two complementary hypotheses are under debate: an electrostatically-triggered orbital polarization at the superconductor surface [5,11], or the injection of highlyenergetic quasiparticles extracted from the gate [7,12]. Here, we tackle this crucial issue via a fully suspended gate-controlled Ti nano-transistor.…”

Vanadium gate-controlled Josephson half-wave nanorectifier

“…In the last few years, the possibility to suppress the critical current in conventional Bardeen-Cooper-Schrieffer (BCS) superconducting wires 1 , Dayem bridge (DB) Josephson junctions (JJs) [2][3][4][5] and superconductor-normal metalsuperconductor weak-links 6 via electrostatic gating was demonstrated 7 . Such a technique is at the basis of a class of innovative all-metallic superconducting Josephson transistors, where a gate electrode is used to modulate down to full suppression the critical current of a superconducting channel, in analogy to what occurs for the current in standard gated semiconductor transistors.…”

“…So far, the microscopic origin of the gating effect in metallic superconductors is still unclear, and the debate in the search of a satisfactory explanation for the aforementioned phenomenology has just started. 4,10,11 . Yet, several technological implementations based on gated superconducting transistors for both classical and quantum computation architectures were proposed 7 til now, and promise new paradigms to realize innovative superconducting circuits.…”