Abstract
On a Pb(111) superconducting surface, low temperature dI/dV tunnelling spectra are recorded between two scanning tunnelling microscopes (STM) metallic tips with the Pb(111) sample metallic support non-grounded. The tunnelling current intensity I passing between the 2 tips through the sample is controlled by changing one or both STM vacuum tunnelling junction resistances. The chemical potential of this floating Pb(111) surface depends on the normalized ratio between those two quantum resistances. When ungrounded, the Pb(111) sample chemical potential balances between those of the 2 STM tips while tuning their respective tip end atomic apex to Pb(111) surface distances with a picometer precision without any physical contact between the STM tips and the surface.
Highlights
In a multiple contact electrodes set–up fabricated on the surface of a conductive material to characterize, for example, its intrinsic electronic transport properties, the different chemical potentials of the source, drain and/or floating electrodes are governing the current intensities passing through the sample [1]
And on the sample surface, the lateral and vertical positioning of the scanning tunnelling microscopes (STM) tip electrodes is controlled within a few nanometers
We demonstrate how mS can be tuned in real time by setting the two STM tips distance from the Pb (111) surface with a few picometers precision on our LTUHV 4-STM required to master those non-invasive tunnel contacts
Summary
In a multiple contact electrodes set–up fabricated on the surface of a conductive material to characterize, for example, its intrinsic electronic transport properties, the different chemical potentials of the source, drain and/or floating electrodes are governing the current intensities passing through the sample [1]. In this case and when the sample is not grounded, its surface is set in an electronic floating configuration with still electrons able to be transferred from one STM tip to another through the surface In this configuration explored below, there is a non-classical potential drop due to decoherence effects at each tip apex to surface vacuum tunnelling junction. This strictly noninvasive measurement configuration is to be found when the electronic orbitals overlap between the sample surface and the STM end atom tip apex are maintained as small as possible while conserving long range electron transfer events between the tips through the surface. We demonstrate how mS can be tuned in real time by setting the two STM tips distance from the Pb (111) surface with a few picometers precision on our LTUHV 4-STM required to master those non-invasive tunnel contacts
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