On the origin of the controversial electrostatic field effect in superconductors

Abstract

Superconducting quantum devices offer numerous applications, from electrical metrology and magnetic sensing to energy-efficient high-end computing and advanced quantum information processing. The key elements of quantum circuits are (single and double) Josephson junctions controllable either by electric current or magnetic field. The voltage control, commonly used in semiconductor-based devices via the electrostatic field effect, would be far more versatile and practical. Hence, the field effect recently reported in superconducting devices may revolutionise the whole field of superconductor electronics provided it is confirmed. Here we show that the suppression of the critical current attributed to the field effect, can be explained by quasiparticle excitations in the constriction of superconducting devices. Our results demonstrate that a miniscule leakage current between the gate and the constriction of devices perfectly follows the Fowler-Nordheim model of electron field emission from a metal electrode and injects quasiparticles with energies sufficient to weaken or even suppress superconductivity.

Gate-Controlled Supercurrent in Epitaxial Al/InAs Nanowires

“…Assuming that the leakage takes place between the gate electrode and the nanowire, in the simplest ballistic picture, hot electrons are injected into the superconducting shell with energies even as high as 10–20 eV, which is several orders of magnitude higher than the SC gap. These electrons could heat up the superconducting bridge and drive it to the normal state, as it is proposed by refs ( 22 − 24 ) as a microscopic origin of the gating effect. Our basic estimation (see the Supporting Information ) of induced heat transfer also suggests that the hot electrons could bring the temperature of the epitaxial shell in the range of the superconducting critical temperature.…”

“…In previous studies, the origin of GCS was attributed to two different mechanisms, either to the effect of the applied electric field 12 − 21 , 25 − 28 or to high-energy quasiparticle injection via tunneling. 22 − 24 We will compare our experimental findings with these explanations in the following.…”

“… 12 , 15 We also note that a large scattering in the critical currents values was observed in the measurements at V BG > 17 V, which can be attributed to the wide nonthermal switching current distribution as a result of the gating effect. 19 , 24 , 39 , 46…”

“…In superconducting nanobridges the supercurrent can be controlled by applying a voltage on a closely spaced gate electrode. 12 − 24 By increasing the gate voltage beyond a certain threshold, the supercurrent in the nanobridge can be quenched. Previous works show GCS in thin metallic nanowires, 12 , 18 , 22 , 23 in proximitized normal metal in a superconductor–normal–superconductor (SNS) junction 13 and in Dayem nanobridges.…”

Zero magnetic-field orbital vortices in s-wave spin-singlet superconductors

“…Non-centrosymmetric superconductors manifest unconventional phenomena, including parity mixing of spin-singlet and spin-triplet pairs [16,17], magnetoelectric effects [18,19], unconventional Andreev states [20,21], and topological phases [22][23][24]. As it concerns electrical manipulation of ultrathin metallic superconductors, the recent observations [25] of the suppression of critical supercurrent by gating and of other anomalous findings [26][27][28][29][30][31][32][33][34], further underline a profound complexity, not yet fully uncovered, behind the coupling between superconductivity, inversion symmetry breaking, and electric fields.…”