Imaging doubled shot noise in a Josephson scanning tunneling microscope

Abstract

We have imaged the current noise with atomic resolution in a Josephson scanning tunneling microscope with a Pb-Pb junction. By measuring the current noise as a function of applied bias, we reveal the change from single electron tunneling above the superconducting gap energy to double electron charge transfer below the gap energy when Andreev processes become dominant. Our spatially resolved noise maps show that this doubling occurs homogeneously on the surface, also on impurity locations, demonstrating that indeed the charge pairing is not influenced by disruptions in the superconductor smaller than the superconducting coherence length.

Superconducting Scanning Tunneling Microscope Tip to Reveal Sub-millielectronvolt Magnetic Energy Variations on Surfaces

“…42 The surface superconducting gap appears at ∆ tip + ∆ substrate ≈ 2∆ in the dI/dV spectra, due to the convolution with the tip electronic structure. [33][34][35][36] This is confirmed by the two QP peaks appearing at ±2.55±0.02 mV in Fig. 1 (c).…”

“…Its excitation efficiency is however one order of magnitude bigger, and is then interesting to study the variation of magnetic IETS with molecular interactions. 31,32 Here, we use the enhanced energy resolution of a superconducting STM tip [33][34][35][36] to reveal the small magnetic changes on a molecular-magnet layer. We focus our attention onto a prototypical molecular magnet, nickelocene (Nc), and on the vdW-governed arrays it forms on Pb (111).…”

“…Figure 1 (a) shows a constant current STM image of the Pb (111) surface taken with Nc at the tip apex of the superconducting tip. The molecular tip gives an enhanced spatial resolution [33][34][35][36] that permits us to discriminate among top (black dot), hollow (red and green dots) and bridge (orange dot) sites. To further distinguish HCP from FCC hollow sites, we 3 The quasiparticle (QP) peak consistently appears at 2.61 ± 0.02 mV, but (g) the inelastic peak depends on the measured molecules (the uncertainty has been determined from the variance of the measurements over 45 molecules).…”

Spatially dispersing Yu-Shiba-Rusinov states in the unconventional superconductor FeTe0.55Se0.45

“…How such states are related to the topological superconductivity in FeTe 0.55 Se 0.45 remains an open question. Our work further shows that one needs to be careful when interpreting zero-bias peaks in putative topological states, and junction resistance dependent experiments are a necessary—ideally combinded with other techniques such as noise spectroscopy 65 – 67 (see also Supplementary Note 4 ), spin-polarized STM 68 , or photon-assisted tunneling 69 will allow for better understanding. Independent of this, tunable impurity states like the one we report here could offer a platform to study quantum phase transitions, impurity scattering, and the screening behavior of superfluids.…”

Spatial and energy resolution of electronic states by shot noise

“…Consequently, the energy resolution of such a measurement is only limited by the bath temperature. The spatial resolution is virtually unlimited with state-of-the-art noise scanning techniques [6,[53][54][55]. The approach is quite universal and equally suitable for the measurements of the nonequilibrium configurations created by charge, spin [56] and valley, etc.…”