Hermann Suderow

IFIMAC, Universidad Autónoma de Madrid, Spain

The feedback driven atomic scale Josephson microscope

The Scanning Tunneling Microscope provides is often used to study the tunneling conductance as a function of the position at atomic scale. We often expect to see things like those we know from macroscopic experiments. For example, we know that junctions between two superconductors present the Josephson effect, or that application of a magnetic field leads to Landau quantization in the electronic density of states. However, the behavior at atomic scale can be notoriously different from the one observed at macroscopic scale, because of the small size of the tunnel junction. Here I will present two examples of new behavior characteristic of ultra small junctions. First, I will discuss the Feedback driven atomic scale Josephson microscope, which is based on a new Josephson junction regime in between the usual DC Josephson effect and the resistive state. The regime consists of a time dependent behavior, in between DC and microwave Josephson frequencies. The Feedback driven atomic scale Josephson microscope provides a ten-fold enhancement of the signal to noise ratio and new switching behavior at a non-zero bias voltage, which we have used it to analyze the pair density wave in NbSe2. Then, I will present the conditions required to observe Landau quantization at atomic scale and results showing the linear dispersion relation connected to Weyl type II cones in the semimetal WTe2.