7 research outputs found
Manipulating quantum Hall edge channels in graphene through Scanning Gate Microscopy
We show evidence of the backscattering of quantum Hall edge channels in a
narrow graphene Hall bar, induced by the gating effect of the conducting tip of
a Scanning Gate Microscope, which we can position with nanometer precision. We
show full control over the edge channels and are able, due to the spatial
variation of the tip potential, to separate co-propagating edge channels in the
Hall bar, creating junctions between regions of different charge carrier
density, that have not been observed in devices based on top- or split-gates.
The solution of the corresponding quantum scattering problem is presented to
substantiate these results, and possible follow-up experiments are discussed.Comment: 10 pages, 12 figure
Electrostatic field-driven supercurrent suppression in ionic-gated metallic Josephson nanotransistors
Recent experiments have shown the possibility to tune the electron transport
properties of metallic nanosized superconductors through a gate voltage. These
results renewed the longstanding debate on the interaction between intense
electrostatic fields and superconductivity. Indeed, different works suggested
competing mechanisms as the cause of the effect: unconventional electric
field-effect or quasiparticle injection. By realizing ionic-gated Josephson
field-effect nanotransistors (IJoFETs), we provide the conclusive evidence of
electrostatic field-driven control of the supercurrent in metallic nanosized
superconductors. Our Nb IJoFETs show bipolar giant suppression of the
superconducting critical current up to with negligible variation of
both the critical temperature and the normal-state resistance, in a setup where
both overheating and charge injection are impossible. The microscopic
explanation of these results calls upon a novel theory able to describe the
non-trivial interaction of static electric fields with conventional
superconductivity.Comment: 9 pages, 6 figure
Unveiling mechanisms of electric field effects on superconductors by a magnetic field response
We demonstrate that superconducting aluminium nanobridges 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 described within a microscopic model where a spatially uniform interband 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